阅读说明：本技术 用便携式装置认证磁感应标记的方法 (Method for authenticating magnetic induction marks with a portable device ) 是由 T·迪诺伊伍 J-L·多里耶 E·豪拉斯 E·洛吉诺夫 C-A·德斯普兰德 A·卡利加里 于 2020-02-10 设计创作，主要内容包括：本发明涉及一种用便携式装置认证磁感应标记的方法,磁感应标记施加在基板上并且包括磁定向的部分反射片状磁性或可磁化颜料颗粒,便携式装置配备有可操作以递送可见光的光源、成像器、处理器和存储器,方法包括：用处理器计算由部分反射片状磁性或可磁化颜料颗粒反射并且由处于相应视角θ的成像器收集的光的相应平均强度I；存储所计算的反射光的平均强度以及相应视角以获得反射光强度曲线I(θ)；将所存储的反射光强度曲线I(θ)与所存储的针对磁感应标记的参考反射光强度曲线I-(ref)(θ)进行比较,以及基于比较的结果来确定磁感应标记是否真实。(The invention relates to a method of authenticating a magnetically inductive marker applied on a substrate and comprising magnetically oriented, partially reflective, flake-like, magnetic or magnetizable pigment particles with a portable device equipped with a light source operable to deliver visible light, an imager, a processor and a memory, the method comprising: calculating, with a processor, respective average intensities I of light reflected by the partially reflective flake-like magnetic or magnetizable pigment particles and collected by the imager at respective viewing angles θ; storing the calculated average intensity of the reflected light and the corresponding viewing angle to obtain a reflected light intensity curve I (θ); comparing the stored reflected light intensity curve I (theta) with a stored reference reflected light intensity curve I for the magnetic induction marks ref (theta) making a comparison, and determining magnetically induced markings based on the result of the comparisonWhether it is true.)

1. A method of authenticating a magnetically inductive marker (1) with a portable device, the magnetically inductive marker (1) being applied on a substrate (2) and comprising a region with a planar layer of a material comprising magnetically oriented, partially reflective flake-like magnetic or magnetizable pigment particles (6), the portable device being equipped with a light source (5) operative for delivering visible light, an imager (4), a processor and a memory, the method comprising:

-arranging an imager of the portable device to face the region of the magnetically induced indicia;

-illuminating a region of the magnetically inductive label with the light source by moving the imager over the magnetically inductive label in the direction of orientation of the magnetic or magnetizable pigment particles and parallel to the planar layer, and taking a plurality of digital images of the illuminated region with the imager, wherein for each different digital image the imager is at a respective different viewing angle θ relative to the region;

-calculating, with the processor, for each digital image, a respective average intensity I of light (8) reflected by the partially reflective platy magnetic or magnetizable pigment particles and collected by the imager at a respective viewing angle θ;

-storing the calculated average intensity of the reflected light and the corresponding viewing angle to obtain a reflected light intensity curve I (θ);

-comparing the stored reflected light intensity curve I (θ) with a stored reference reflected light intensity curve I (θ) for the magnetic induction marks_ref(theta) are compared, and

-determining whether the magnetically induced marker is authentic based on the result of the comparison.

2. The method of claim 1, further comprising:

-calculating the rate of change of the reflected light intensity curve I (θ) to determine the angular value of the curve and the corresponding intensity peak;

-comparing the calculated angle value and intensity peak value with a stored reference angle value and reference intensity peak value for the magnetic induction marks, respectively,

wherein determining whether the magnetically responsive marker is authentic is further based on the result of the comparison.

3. The method of claim 1, further comprising:

-calculating from the acquired digital image a variance of the intensity of the reflected light on the region of the magnetically inductive marker;

-comparing the calculated variance with a reference variance value for the magnetic induction markers,

wherein determining whether the magnetically responsive marker is authentic is further based on the result of the comparison.

4. The method according to any one of claims 1 to 3, further comprising reading a geometric reference pattern at least partially overlapping the region of the magnetically inductive marking and in the form of a coded marking selected from coded alphanumeric data, a one-dimensional barcode, a two-dimensional barcode, a QR code (12) or a data matrix.

5. The method according to any of the preceding claims, wherein the regions of magnetically induced markings comprise co-parallel magnetically oriented partially reflective flake-like magnetic or magnetizable pigment particles.

6. Method according to any of the preceding claims, wherein the regions of the magnetically induced marks comprise first regions and second regions, the first regions comprising magnetically oriented partially reflective plate-like magnetic or magnetizable pigment particles (6) that are co-parallel in one first direction, and the second regions having partially reflective plate-like magnetic or magnetizable pigment particles (6') that are oriented in a second direction different from the first direction.

7. The method according to any of the preceding claims, wherein the portable device is a smartphone (3) or a tablet.

8. A portable device for authenticating a magnetically inductive marker (1), wherein the magnetically inductive marker (1) is applied on a substrate (2) and comprises a region with a planar layer of a material comprising magnetically oriented, partially reflective, plate-like magnetic or magnetizable pigment particles (6), the portable device comprising:

a light source (5) operative for delivering visible light (7) and illuminating the region of the magnetically induced indicia,

an imager (4) operative for taking a plurality of digital images of the illuminated area while moving over the magnetically inductive marker in the direction of orientation of the magnetic or magnetizable pigment particles and parallel to the planar layer, wherein, for each different digital image, the imager is at a respective different viewing angle θ relative to the area,

a memory for storing the calculated average intensity of the reflected light (8) and the corresponding viewing angle to obtain a reflected light intensity curve I (theta), an

A processor operative to compare the stored reflected light intensity curve I (θ) with a stored reference reflected light intensity curve I for the magnetic induction marks_ref(θ) comparing, and determining whether the magnetic induction mark is authentic based on a result of the comparison.

9. Apparatus according to claim 8, wherein the processor is operative to calculate a rate of change of the reflected light intensity curve I (θ) to determine an angle value and a corresponding intensity peak value of the curve, compare the calculated angle value and intensity peak value with a stored reference angle value and reference intensity peak value for the magnetic induction marking, respectively, and determine whether the magnetic induction marking is authentic further based on the result of the comparison.

10. The apparatus of claim 8 wherein the processor is operative to calculate a variance of reflected light intensity over the region of the magnetic induction marking from the acquired digital image, compare the calculated variance to a reference variance value for the magnetic induction marking, and determine whether the magnetic induction marking is authentic based further on a result of the comparison.

11. The device of any one of claims 8 to 10, further operative for reading a geometric reference pattern at least partially overlapping the region of the magnetically inductive marker and in the form of a coded marker selected from a one-dimensional barcode, a two-dimensional barcode, a QR code (12) or a data matrix of coded alphanumeric data.

12. A device according to any of claims 8 to 11, wherein the regions of magnetically induced markings comprise co-parallel magnetically oriented partially reflective flake-like magnetic or magnetizable pigment particles.

13. A device according to any of claims 8-12, wherein the regions of the magnetically induced marks comprise first and second regions, the first region comprising magnetically oriented partially reflective plate-like magnetic or magnetizable pigment particles (6) that are co-parallel in one first direction, and the second region having partially reflective plate-like magnetic or magnetizable pigment particles (6') that are oriented in a second direction different from the first direction.

14. The device according to any of claims 8 to 13, wherein the portable device is a smartphone (3) or a tablet.

15. A non-transitory computer readable medium comprising computer code portions executable by a processor to cause a portable device equipped with a light source (5) and an imager (4) operative to deliver visible light (7) to perform the method according to any one of claims 1-7.

Technical Field

The present application relates to a method for authenticating a mark on a substrate, said mark being printed with an ink comprising magnetic or magnetizable pigment particles, and to a portable device, preferably a smartphone, for implementing said method.

Background

It is known in the art to produce security elements in the form of magnetically induced markings, for example in the field of security documents, using inks, compositions, coatings or layers comprising oriented magnetic or magnetizable pigment particles, in particular also optically variable magnetic or magnetizable pigment particles. Coatings or layers comprising oriented magnetic or magnetizable pigment particles are disclosed for example in US 2,570,856, US 3,676,273, US 3,791,864, US 5,630,877 and US 5,364,689. Coatings or layers comprising oriented magnetic color-changing pigment particles have been disclosed in WO 2002/090002 a2 and WO 2005/002866 a1, resulting in particularly attractive optical effects useful for the protection of security documents.

The magnetic or magnetizable pigment particles in the printing ink or coating allow the creation of magnetically induced marks, designs and/or patterns by applying a corresponding magnetic field, thereby causing local orientation of the magnetic or magnetizable pigment particles in the unhardened coating, which is subsequently hardened. The result is a fixed magnetically induced mark, design or pattern. Materials and techniques for orienting magnetic or magnetizable pigment particles in coating compositions have been disclosed in US 2,418,479, US 2,570,856, US 3,791,864, DE 2006848-A, US 3,676,273, US 5,364,689, US 6,103,361, EP 0406667B 1, US 2002/0160194, US 2004/70062297, US 2004/0009308, EP 0710508 a1, WO 2002/09002 a2, WO 2003/000801 a2, WO 2005/002866 a1, WO 2006/061301 a 1. These documents are incorporated herein by reference. In this way, a highly forgery-resistant magnetically induced marking can be produced. The magnetic inductive marking thus obtained results in an angular reflection distribution which is substantially asymmetric with respect to the normal of the substrate to which the magnetic inductive marking is applied. This is unusual and differs from the classical specular or Lambertian reflection/scattering behavior.

For example, security features for security documents can generally be classified as "covert" security features on the one hand and "overt" security features on the other hand. The protection provided by covert security features relies on the concept that such features are difficult to detect, often requiring specialized equipment and knowledge for detection, while "overt" security features rely on the concept that is readily detectable with, for example, unaided human perception, e.g., such features may be visible and/or detectable via the touch while still being difficult to produce and/or reproduce. Magnetically induced markings are typically used as "overt" (or level 1) security features that should allow direct and unambiguous authentication by a human without any external device or tool. However, the effectiveness of overt security features depends to a large extent on their easy identification as security features, since most users actually only (and especially those users who do not have prior knowledge of the security features of the document or the item they protect) conduct security checks based on the security features under their existing and natural actual knowledge.

Even if the security level of magnetically sensitive indicia is high in terms of copy resistance, the average consumer may potentially confuse what exact effect should be viewed on a given product for a particular overt security element. In particular, generating a flip hologram (low security, low cost security element) that resembles a pattern or logo may lead to a misleading authenticity for untrained consumers, as it will also generate an angle dependent reflection pattern.

In recent years, many authentication methods using smart phones have emerged. Most of them rely on imaging capabilities of smart phone cameras to extract geometric or topological information below human eye resolution (such as disclosed in WO 0225599 a1), or beyond the ability of humans to extract signals very close to noise or to account for weak variations in printed design colors or shapes (such as disclosed in WO 2013071960 a 1). These methods have the advantage of extracting the encoded information for identification, but on the other hand require high resolution printing and/or magnifying optics attached to the smartphone camera.

Other authentication methods suitable for low resolution printed features have been developed which rely on colorimetric analysis of security features (as disclosed in US 2011190920), are based on holograms (or SICPASMART such as disclosed in WO 2015052318 a1)^TM) Which analyzes the color change characteristics of the optically variable pattern measured during the augmented reality assisted azimuth displacement of the smartphone around the pattern. These methods rely on the movement of the smartphone camera relative to the markers, which is complex to implement. Furthermore, these approaches are dependent on external light illumination and are therefore highly sensitive to ambient light conditions (e.g., direct sunlight, dark environments, or highly chromatically unbalanced illumination).

Other authentication methods with features of angle-dependent reflection intensity have been proposed, such as randomly oriented lamellae (as disclosed in WO 2012136902 a1 and US 20140224879), micro mirrors, diffractive features (like holograms or embossed 3D structures) (as disclosed in WO 2015193152 a1 or US 2016378061). These methods are based on two angular positions of the camera used to capture two images (which are then analyzed).

Controlling both the camera of the smartphone and the sample illumination to obtain a reproducible measurement of the reflectance of the security feature remains a challenge. Smart phone cameras typically use auto-exposure and focus algorithms suitable for typical camera use (e.g., landscape or portrait photographs), but such algorithms are not suitable for imaging highly reflective markers with magnetically induced markers. Illumination of the security feature may result from ambient lighting, either indoors or outdoors, which is often unknown and difficult to control, and may prevent reliable detection of a particular security feature (such as angular reflectivity) of the magnetically-induced indicia.

Thus, currently known smartphone-based authentication techniques have a number of drawbacks, including the following: they require high resolution printing of fine structures; and/or they rely on sophisticated smartphone movement to reveal color; and/or they cannot reliably authenticate accurately with precise angular dependence due to limited available information (e.g., the method of using only two angular positions of a camera in the prior art).

It is therefore desirable to propose to the public, and potentially also to relevant inspectors, an improved, accurate and reliable solution robust against ambient light disturbances, which does not rely on high resolution printing or complex movements of a smartphone, and which avoids difficult to control and non-intuitive tilting or azimuthal position or rotational movements.

In particular, there is a need for an authentication method and apparatus that can clearly distinguish a given magnetically induced marker from another magnetically induced marker or from another overt security feature produced with other techniques and from impersonation based on another technique that attempts to impersonate or simulate effects but reproduces the security feature or marker topology and has some angular dependence of the reflection intensity.

It is therefore an object of the present invention to overcome the disadvantages of the prior art by providing a method of using a portable device, preferably a smartphone, to authenticate magnetically induced indicia for use as an overt security feature printed or affixed to a substrate, such as a label, product or document.

It is a further object of the present invention to provide a portable device, preferably a smart phone, for authenticating magnetically induced markings applied to a substrate, which is easy to control, which has good immunity to ambient light variability, and which is highly discriminative for impersonation, and selective for other angle-dependent reflective markings.

It is a further object of the invention to provide a corresponding non-transitory computer readable medium comprising computer code portions or instructions executable by a processor to cause a portable device equipped with a light source and an imager to perform an authentication method as described herein.

Disclosure of Invention

According to one aspect, the invention relates to a method of authenticating a magnetically inductive marker on a substrate with a portable device, the magnetically inductive marker comprising a region having a planar layer of a material comprising magnetically oriented, partially reflective flake-like magnetic or magnetizable pigment particles, the portable device being equipped with a light source operable to deliver visible light, an imager, a processor and a memory, the method comprising:

-positioning an imager of the portable device at a given distance L above the region of magnetically induced markers;

-illuminating a region of the magnetically induced marker with the light source by moving the imager over the marker in a direction parallel to the planar layer, and taking a plurality of digital images of the illuminated region with the imager, wherein for each different digital image the imager is at a respective different viewing angle θ relative to the region;

-calculating, with the processor, for each digital image, a respective average intensity I of light (8) reflected by pigment particles and collected by the imager at a respective viewing angle θ;

-storing the calculated average intensity of the reflected light and the corresponding viewing angle to obtain a reflected light intensity curve I (θ);

-comparing the stored reflected light intensity curve I (θ) with the stored reference reflected light intensity curve I (θ) for the magnetic induction marks_ref(theta) are compared, and

-determining whether the magnetically induced marker is authentic based on the result of the comparison.

According to an aspect of the invention, the imager of the portable device is a camera, preferably a smartphone camera. In particular, the method takes advantage of the geometric arrangement of the smartphone camera and its built-in flash, which allows flash-to-camera reflection by partially reflecting flake-like magnetic or magnetizable pigment particles to be selectively obtained for specific locations of the smartphone body. The position is predetermined by knowledge and control of the precise grain azimuth, knowledge of camera zoom and flash-to-camera distance, and a specified camera-to-mark distance.

In this way, for example, a magnetically induced mark with a given angle of orientation of partially reflective plate-like magnetic or magnetizable pigment particles can be accurately distinguished from another mark with a different angle of orientation of the particles or a mark producing a similar effect, based on a holographic film or on a design based on micro mirrors. Using flash illumination having a known position relative to the camera reduces the effect of ambient illumination on the measurement and improves the accuracy of the authentication. In addition, a suitable graphical user interface provides guidance to the user (such as a target on the smartphone display, etc.) to accurately position the smartphone in the correct location. The sequence of images of the magnetically induced marker is then acquired with the flash on, while the smartphone is moved parallel to the plane of the marker at a prescribed distance. The sequence of images is then analyzed by an image processing algorithm to extract the reflection areas from the marker or the local intensity pattern comprising the marker or a part thereof. For example, the image processing algorithm comprises extracting intensity values from at least one predetermined area (region) of the image corresponding to a particular design of the magnetically induced markers expected from the reflection intensity of partially reflective flake-like magnetic or magnetizable pigment particles, or not for a given security image design and the position of the smartphone relative to the image. The intensity values (levels) of these regions are used as a criterion as a function of position (and viewing angle) to determine whether the magnetically induced markers are authentic. In one embodiment, the stored reflected light intensity curve I (θ) is compared to a stored reference reflected light intensity curve I (θ) for the image_ref(θ) comparing and determining whether the magnetic induction marking is authentic based on the result of the comparison (i.e., the matching of the curves within a given tolerance criterion). Preferably, a reference reflected light intensity curve I for the magnetic induction marks_ref(θ)Stored in the memory of the portable device or connectable to a remote server of the portable device via any communication means.

In another aspect of the invention, the method includes calculating a rate of change of the reflected light intensity curve I (θ) to determine an angle value and a corresponding value of an intensity peak of the curve; comparing the calculated angle value and intensity peak value with a stored reference angle value and reference intensity peak value for the magnetic induction marks, respectively. In this case, it is further determined whether the magnetic induction mark is authentic based on the result of the comparison. Preferably, the reference angle values and the reference intensity peaks for said magnetic induction markers are stored in a memory of the portable device or connectable to a remote server of the portable device via any communication means.

In other words, the reflection intensity distribution (equivalent to angular variation) can be extracted as a function of position, and can be converted into an angular reflection distribution that contains additional specific information that can be used as authentication criteria (such as distribution width, peak position, skew, asymmetry, turning points and other features, etc.). The distribution can be fed into a machine learning algorithm (e.g., a decision tree) to define rules for authentication that use features in the distribution that are specific to the magnetic induction markers.

In another aspect of the invention, the method further comprises calculating a variance of reflected light intensity over said region of the magnetic induction marking from the acquired digital image, comparing the calculated variance with a reference variance value for said image, wherein it is determined whether the magnetic induction marking is authentic further based on the result of said comparison. Preferably, the reference variance values of the magnetic induction marks are stored in a memory of the portable device or connectable to a remote server of the portable device via any communication means.

Some reference background printed areas that produce lambertian (symmetric) reflection/scattering behavior may also be used to make intensity corrections and account for potential illumination non-uniformities, illumination variations due to variable distances of the sample, or variations in image acquisition parameters such as gain or exposure time.

A geometric reference pattern of known shape and dimensions can be printed near or over the image of the partially reflective flake-like magnetic or magnetizable pigment particles to allow magnetic inductive markings on the substrate to be found, to make perspective corrections, and to correct for small changes in smartphone distance or tilt relative to the substrate during scanning.

Thus, the method further comprises reading a geometric reference pattern that at least partially overlaps the region of the magnetically induced indicia and is in the form of a coded indicia (such as a coded alphanumeric data, a one-dimensional barcode, a two-dimensional barcode, a QR code, or a data matrix, etc.). Furthermore, this allows the security mark to be identified for traceability purposes. The geometric reference pattern becomes fully readable only at certain angular values corresponding to non-specular reflection of the illumination light, such that the regions appear as a uniform background, allowing the device to decode the pattern.

According to one embodiment, at least one region of the magnetically inductive marking comprises co-parallel (co-parallel) magnetically oriented partially reflective plate-like magnetic or magnetizable pigment particles. The zones thus exhibit overt security features that produce a substantially asymmetric reflected intensity distribution relative to the normal to the substrate. This orientation pattern is known as the louvre effect, in which the plate-like magnetic or magnetizable pigment particles have magnetic axes parallel to each other and to a plane, which is not parallel to the substrate to which the particles are applied. In particular, an optical effect, wherein the partially reflective plate-like magnetic or magnetizable pigment particles are parallel to each other and have substantially the same pigment particle plane elevation angle of at least 30 ° relative to the plane of the substrate to which the particles are applied. Methods for producing the louvre effect are disclosed, for example, in us 8,025,952 and european 1819525B1

Alternatively or additionally, the magnetically oriented indicia comprises a first region comprising magnetically oriented partially reflective platy magnetic or magnetizable pigment particles that are co-parallel in one first direction and a second region having partially reflective platy magnetic or magnetizable pigment particles that are oriented in a second direction different from the first direction. The effect obtained with this orientation pattern is called flip effect, where the mark comprises a first portion and a second portion separated by a transition portion, where in the first portion the particles are aligned parallel to the first plane and in the second portion the particles are aligned parallel to the second plane. Methods for generating the flip effect are disclosed, for example, in EP 1819525B1 and EP 1819525B 1. In this case, preferably, the image processing algorithm comprises extracting intensity values from two predetermined regions of the magnetic induction markers during the sequence of images (e.g. video) as a function of the position of the images relative to the smartphone. In particular, the rate of change of intensity from each of the two regions of the magnetically induced marks as a function of the image position is extracted.

In another aspect, the invention provides a portable device for authenticating a magnetically induced mark on a substrate, the magnetically induced mark comprising a region having a planar layer of a material comprising oriented partially reflective flake-like magnetic or magnetizable pigment particles, the device comprising:

a light source operable to deliver visible light and illuminate a region of the magnetically-induced indicia,

an imager operable to take a plurality of digital images of the illuminated area while moving over the magnetic induction marks in a direction substantially parallel to the planar layer, wherein the imager is at a respective different viewing angle θ relative to the area for each different digital image,

a memory for storing the calculated average intensity of the reflected light (8) and the corresponding viewing angle to obtain a reflected light intensity curve I (theta), an

A processor operable to compare the stored reflected light intensity profile I (θ) with a stored reference reflected light intensity profile I for the marker_ref(theta) comparing, and determining whether the magnetic induction mark is authentic based on a result of the comparison

In another aspect of the invention, the processor is operable to calculate the rate of change of the reflected light intensity curve I (θ) to determine an angle value and a corresponding intensity peak value of the curve, compare the calculated angle value and intensity peak value with a stored reference angle value and reference intensity peak value for the mark, respectively, and also determine whether the magnetically induced mark is authentic based on the result of the comparison.

In another aspect of the invention, the processor is operable to calculate a variance of reflected light intensity over a region of the magnetic induction marking from the acquired digital image, compare the calculated variance to a reference variance value for the marking, and determine whether the magnetic induction marking is authentic further based on a result of the comparison.

In another aspect of the invention, the device is further operable to read a geometric reference pattern at least partially overlapping the region of the magnetically induced indicia and in the form of a coded indicia selected from a group consisting of a coded alphanumeric data, a one-dimensional barcode, a two-dimensional barcode, a QR code (12) or a data matrix.

In another aspect of the invention, the portable device is a smartphone or tablet.

In another aspect, the invention provides a non-transitory computer readable medium comprising computer code portions or instructions executable by a processor to cause a portable device equipped with a light source and an imager operable to deliver visible light to perform a method of authenticating a badge as described herein.

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which non-limiting, salient aspects and features of the invention are shown.

Drawings

Fig. 1 is a schematic illustration of partially reflective flake-like magnetic or magnetizable pigment particles detecting the magnetic orientation of a magnetically inductive marker by a smartphone due to particle reflection (or non-reflection) depending on their position relative to the marker.

Fig. 2 is an example of a measurement setup with a smartphone and a sample scanned in a plane parallel to the smartphone and at a fixed distance from the smartphone.

Fig. 3 shows a graphical representation of the position and illumination/viewing angle of the magnetic induction markers in the image set, and the intensity distribution for a known smartphone-to-sample distance.

Fig. 4 shows the intensity and relative intensity distribution of magnetic induction markers extracted from a sequence of images.

Fig. 5 is a schematic illustration of a magnetically induced mark having partially reflective flake-like magnetic or magnetizable pigment particles magnetically oriented in two opposite directions.

Fig. 6 shows a specific printed design of an embodiment of the invention comprising magnetically oriented partially reflective plate-like magnetic or magnetizable pigment particles in two different orientations in different regions of the magnetically induced mark (which may also at least partially overlap).

Fig. 7 shows a specific printed design of one embodiment of the present invention comprising magnetically oriented partially reflective flake-like magnetic or magnetizable pigment particles in two different orientations in different regions of magnetic induction.

Fig. 8 is a schematic illustration of the smartphone position on a magnetically inductive tag with two different partially reflective flake-like magnetic or magnetizable pigment particle orientations as shown in fig. 6 or 7 and image frames obtained at these two positions.

Fig. 9 is a schematic illustration of the effect of a magnetic induction marker or a 90 ° rotation of a smart phone in the marker plane and a guide object on a picture.

Fig. 10 is a schematic representation of a magnetically induced marking of a partially reflective platy magnetic or magnetizable pigment particle having a magnetic orientation in the E-direction (particle 1) and another type of particle oriented in the S-direction of 90 ° relative to particle 1 (particle 2).

FIG. 11 is a graphical representation of an intensity distribution, its first and second derivatives, with respect to position.

Fig. 12 is a graphical representation of the intensity cross-section of a magnetically inductive tag at one particular location relative to a smartphone, showing individual partially reflective flake-like magnetic or magnetizable pigment particle reflections.

FIG. 13 is a graphical representation of the distribution of relative intensity and intensity variance as a function of position of magnetically induced markers in an image set, showing similar behavior of relative intensity and variance.

FIG. 14 is a graphical representation of the intensity distribution of various indicia. The distribution of magnetically induced marks clearly shows significant differences from other marks due to their asymmetry with respect to the axis. The relative intensity profile a relates to a magnetic induction mark, the relative intensity profile B is a color-changing pattern composed of nonmagnetic color-changing flake pigment particles, the relative intensity profile C is a pattern composed of ink including silver metal particles, and the intensity profile D relates to only paper.

Fig. 15 shows an example of relative intensity and variance distributions of various types of markers (including magnetic induction markers, holograms, and micromirrors) containing partially reflective flake-like magnetic or magnetizable pigment particles.

FIG. 16 illustrates various embodiments of a magnetically inductive marker.

Fig. 17 illustrates various features of integrating magnetically induced indicia with a QR code.

Detailed Description

In the following, reference will be made to the accompanying drawings in describing various embodiments of the invention. This description is provided to better understand the concepts of the embodiments of the present invention and to point out certain preferred modifications of the general concepts.

It should be noted that a key advantage of the present invention requires some specificity of the magnetic induction markers for robust and reliable authentication, namely:

there should be an acute dependence of the local reflectivity;

the angular dependence should be azimuthally asymmetric with respect to the normal to the marker axis;

the angular dependence should be well controllable by the marking process and determined by the co-parallel alignment of the reflective elements;

the background and the surrounding of the mark should also be controlled.

These requirements may be met by several candidates for security features that are obvious in different applications in the art as security features for banknotes, labels and tax banderoles, or security documents such as passports, checks or credit cards. The main examples of these candidates are:

(A) magnetically inductive indicia comprising oriented partially reflective flake-like magnetic or magnetizable pigment particles;

(B) an arrangement of micro mirrors embossed on a metal substrate or film;

(C) an arrangement of microlenses in an array having a mask over the reflective pattern;

(D) a diffractive structure (such as a holographic foil or an embossed diffractive structure, etc.).

Flake pigment particles are two-dimensional particles due to the large aspect ratio of their dimensions, as compared to acicular pigment particles, which can be considered as one-dimensional particles. Flake-like pigment particles can be considered as two-dimensional structures, wherein dimensions X and Y are substantially larger than dimension Z. Flake-like pigment particles are also known in the art as platelet-like particles or flakes. Such pigment particles can be described as having a major axis X corresponding to the longest dimension intersecting the pigment particle and a second axis Y perpendicular to X that is also located within the pigment particle. The magnetically inductive labels described herein comprise oriented partially reflective flake-like magnetic or magnetizable pigment particles, which due to their shape have a non-isotropic reflectivity. As used herein, the term "isotropic reflectivity" means that the proportion of incident radiation from a first angle, reflected by the particle to a certain (viewing) direction (second angle), is a function of the orientation of the particle, i.e. a change in the orientation of the particle relative to the first angle may result in a different amount of reflection to the viewing direction. Preferably, the partially reflective platelet-shaped magnetic or magnetizable pigment particles described herein have a non-isotropic reflection with respect to incident electromagnetic radiation over some portion or the entire wavelength range from about 200 to about 2500nm (more preferably from about 400 to about 700nm), such that a change in orientation of the particles results in a change in the reflection of the particles into a certain direction. Thus, even per unit area (e.g., per μm)²) Is uniform over the entire surface of the platelet-shaped particle, the reflectivity of the particle is non-isotropic due to the shape of the particle, since the visible area of the particle depends on the direction from which it is viewed. As known to those skilled in the art, the partially reflective flake-like magnetic or magnetizable pigment particles described herein are distinct from conventional pigments that exhibit the same color and reflectivity independent of particle orientation, while the magnetic or magnetizable pigment particles described herein exhibit reflection or color, or both, depending on whether they are reflective or coloredThe particles are oriented.

Examples of partially reflective flake-like magnetic or magnetizable pigment particles described herein include, but are not limited to, pigment particles comprising: a magnetic layer M made of one or more of magnetic metals such as cobalt (Co), iron (Fe), gadolinium (Gd), nickel (Ni), or the like; and magnetic alloys of iron, chromium, cobalt or nickel, wherein the flake-like magnetic or magnetizable pigment particles may be a multilayer structure comprising one or more additional layers. Preferably, the one or more additional layers are: layer A, independently selected from the group consisting of magnesium fluoride (MgF)₂) Silicon oxide (SiO), silicon dioxide (SiO)₂) Titanium oxide (TiO)₂) And aluminum oxide (Al)₂O₃) And one or more of the group consisting of metal oxides; or layer B independently made of one or more selected from the group consisting of metals and metal alloys, preferably from the group consisting of reflective metals and reflective metal alloys, more preferably from the group consisting of aluminum (Al), chromium (Cr) and nickel (Ni), still more preferably aluminum (Al); or a combination of one or more layers a (e.g., layer a described above) and one or more layers B (e.g., layer B described above). Typical examples of the flake-like magnetic or magnetizable pigment particles as the above-mentioned multilayer structure include, but are not limited to, A/M multilayer structures, A/M/A multilayer structures, A/M/B multilayer structures, A/B/M/A multilayer structures, A/B/M/B/A multilayer structures, B/M/B multilayer structures, B/A/M/A multilayer structures, B/A/M/B/A multilayer structures, wherein layer A, magnetic layer M and layer B are selected from these layers described above.

According to one embodiment, at least a part of the partially reflective flake-like magnetic or magnetizable pigment particles described herein are a dielectric layer/reflective layer/magnetic layer/reflective layer/dielectric layer multilayer structure and a dielectric layer/reflective layer/dielectric layer/magnetic layer/reflective layer/dielectric layer multilayer structure, wherein the reflective layer described herein is independently and preferably selected from the group consisting of metals and metal alloys (preferably selected from the group consisting of reflective metals and reflective metal alloys, more preferably selected from the group consisting of aluminum (Al), silver (Ag), copper (Cu), gold (Au), platinum (Pt), tin (Sn), titanium (Ti), palladium (Pd), rhodium (Rh), niobium (Nb), and combinations thereof) Chromium (Cr), nickel (Ni), and alloys thereof, even more preferably selected from the group consisting of: aluminum (Al), chromium (Cr), nickel (Ni), and alloys thereof, and still more preferably aluminum (Al)), wherein the dielectric layer is independently and preferably made of a material selected from the group consisting of magnesium fluoride (MgF), for example₂) Aluminum fluoride (AlF)₃) Cerium fluoride (CeF)₃) Lanthanum fluoride (LaF)₃) Sodium aluminum fluoride (e.g., Na)₃AlF₆) Neodymium fluoride (NdF)₃) Samarium fluoride (SmF)₃) Barium fluoride (BaF)₂) Calcium fluoride (CaF)₂) Metal fluorides such as lithium fluoride (LiF), and silicon oxides such as silicon oxide (SiO), silicon dioxide (SiO)₂) Titanium oxide (TiO)₂) Alumina (Al)₂O₃) Etc. (and more preferably selected from the group consisting of: magnesium fluoride (MgF)₂) And silicon dioxide (SiO)₂) And still more preferably magnesium fluoride (MgF)₂) And the magnetic, magnetic layer preferably comprises nickel (Ni), iron (Fe), and/or cobalt (Co) and/or a magnetic alloy with nickel (Ni), iron (Fe), chromium (Cr), and/or cobalt (Co) and/or a magnetic oxide with nickel (Ni), iron (Fe), chromium (Cr), and/or cobalt (Co). Alternatively, the dielectric/reflective/magnetic/reflective/dielectric multilayer structures described herein may be multilayer pigment particles considered safe for human health and the environment, wherein the magnetic layer comprises a magnetic alloy having a substantially nickel-free composition comprising about 40 wt-% to about 90 wt-% iron, about 10 wt-% to about 50 wt-% chromium, and about 0 wt-% to about 30 wt-% aluminum. Particularly suitable partially reflective flake-like magnetic or magnetizable pigment particles having a multilayer structure of dielectric layer/reflective layer/magnetic layer/reflective layer/dielectric layer include, but are not limited to, MgF₂Al/magnet/Al/MgF₂Wherein the magnetic layer comprises iron, preferably a magnetic alloy or mixture of iron and chromium.

Alternatively, the partially reflective platy magnetic or magnetizable pigment particles described herein can be partially reflective platy color changing magnetic or magnetizable pigment particles, in particular magnetic thin film interference pigment particles. Color changing elements (also known in the art as goniochromatic elements), such as pigment particles, inks, coatings or layers, are known in the field of security printing, exhibit viewing angle or incidence angle dependent colors, and are used to protect security documents from forgery and/or illegal reproduction by commonly available color scanning, printing and copying office equipment.

Magnetic thin-film interference pigment particles are known to the person skilled in the art and are disclosed, for example, in US 4,838,648, WO 2002/073250 a2, EP 0686675B 1, WO 2003/000801 a2, US 6,838,166, WO 2007/131833 a1, EP 2402401 a1 and the documents cited therein. Preferably, the magnetic thin-film interference pigment particles comprise pigment particles having a five-layer fabry-perot multilayer structure and/or pigment particles having a six-layer fabry-perot multilayer structure and/or pigment particles having a seven-layer fabry-perot multilayer structure.

A preferred five-layer fabry-perot multilayer structure consists of a multilayer structure of absorber/dielectric/reflector/dielectric/absorber, wherein the reflector and/or absorber is also a magnetic layer, preferably the reflector and/or absorber is a magnetic layer comprising nickel, iron and/or cobalt and/or a magnetic alloy with nickel, iron and/or cobalt and/or a magnetic oxide with nickel (Ni), iron (Fe) and/or cobalt (Co).

The preferred six-layer fabry-perot multilayer structure consists of a multilayer structure of absorber/dielectric/reflector/magnetic/dielectric/absorber.

A preferred seven-layer fabry-perot multilayer structure consists of a multilayer structure of absorber/dielectric/reflector/magnetic/reflector/dielectric/absorber (such as disclosed in US 4,838,648).

Preferably, the reflective layers of the fabry-perot multilayer structures described herein are independently made of one or more materials (such as those described above, etc.). Preferably, the dielectric layers of the fabry-perot multilayer structure are independently made of one or more materials (such as those described above, etc.)

Preferably, the absorption layer is separately made of one or more selected from the group consisting of aluminum (Al), silver (Ag), copper (Cu), palladium (Pd), platinum (Pt), titanium (Ti), vanadium (V), iron (Fe), tin (Sn), tungsten (W), molybdenum (Mo), rhodium (Rh), niobium (Nb), chromium (Cr), nickel (Ni), a metal oxide thereof, a metal sulfide thereof, a metal carbide thereof, and a metal alloy thereof (more preferably, selected from the group consisting of chromium (Cr), nickel (Ni), a metal oxide thereof, and a metal alloy thereof, and still more preferably, selected from the group consisting of chromium (Cr), nickel (Ni), and a metal alloy thereof).

Preferably, the magnetic layer includes a magnetic alloy including nickel (Ni), iron (Fe), and/or cobalt (Co) and/or having nickel (Ni), iron (Fe), and/or cobalt (Co) and/or a magnetic oxide having nickel (Ni), iron (Fe), and/or cobalt (Co). While magnetic thin film interference pigment particles comprising a seven-layer Fabry-Perot structure are preferred, it is particularly preferred that the magnetic thin film interference pigment particles comprise a material consisting of Cr/MgF₂/Al/Ni/Al/MgF₂A seven-layer Fabry-Perot absorption layer/dielectric layer/reflection layer/magnetic layer/reflection layer/dielectric layer/absorption layer multilayer structure composed of/Cr multilayer structures.

The magnetic thin film interference pigment particles described herein may be multilayer pigment particles that are considered safe for human health and the environment and are based on, for example, five-layer fabry-perot multilayer structures, six-layer fabry-perot multilayer structures, and seven-layer fabry-perot multilayer structures, wherein the pigment particles comprise one or more magnetic layers comprising a magnetic alloy having a substantially nickel-free composition comprising about 40 wt-% to about 90 wt-% iron, about 10 wt-% to about 50 wt-% chromium, and about 0 wt-% to about 30 wt-% aluminum. A typical example of multilayer pigment particles considered safe for human health and the environment can be found in EP 2402402401 a1 (which is herein incorporated by reference in its entirety).

The dielectric/reflective/magnetic/reflective/dielectric multilayer structures described herein, the absorber/dielectric/reflective/dielectric/absorber multilayer structures described herein, the absorber/dielectric/reflective/magnetic/dielectric/absorber multilayer structures described herein, and the absorber/dielectric/reflective/magnetic/reflective/dielectric/absorber multilayer structures described herein are typically fabricated by conventional deposition techniques that deposit the various desired layers onto the web. After depositing the required number of layers, for example by Physical Vapor Deposition (PVD), Chemical Vapor Deposition (CVD) or electrolytic deposition, the layer stack is removed from the web by dissolving the release layer in a suitable solvent or by stripping material from the web. The material thus obtained is then broken down into flake-like magnetic or magnetizable pigment particles, which have to be further processed by milling, grinding (such as e.g. a jet-grinding process) or any suitable method to obtain pigment particles of the desired size. The resulting product consists of flaky magnetic or magnetizable pigment particles with broken edges, irregular shapes and different aspect ratios. Further information on the preparation of suitable pigment particles can be found, for example, in EP 1710756a1 and EP 1666546a1 (which are incorporated herein by reference).

The magnetically responsive markers described herein are prepared by a method comprising the steps of: applying a coating composition comprising partially reflective platy magnetic or magnetizable pigment particles as described herein on a substrate; exposing the coating composition to a magnetic field of a magnetic field generating device, thereby orienting at least a portion of the partially reflective platy magnetic or magnetizable pigment particles; and hardening the coating composition to fix the pigment particles in the position and orientation in which they are employed. A detailed description of these steps of treatment with a coating composition can be found in the following patent documents and related references therein: US 2016176223 and US 2003170471.

The applying step described herein is performed by a printing process preferably selected from the group consisting of: screen printing, rotogravure printing and flexographic printing. These methods are well known to the person skilled in the art and are described, for example, in the printing technique j.m. adams and p.a. dolin, delmr Thomson Learning (5 th edition, pages 293, 332 and 352).

After, simultaneously with or simultaneously with the application of the coating composition onto the substrate, the partially reflective flake-like magnetic or magnetizable pigment particles are oriented by using an external magnetic field to orient them according to a desired orientation pattern. The orientation pattern thus obtained may be any pattern.

A wide variety of magnetically induced markers can be produced by different methods as disclosed for example in US 6,759,097, EP 2165774 a1 and EP 1878773B 1. An optical effect known as the rolling bar effect may also be produced. The rolling bar effect shows one or more contrast bands that appear to move ("roll") when the image is tilted relative to the viewing angle, the optical effect being based on a particular orientation of magnetic or magnetizable pigment particles that are aligned in a curved manner, following either a convex curvature (also referred to in the art as a negative-curved orientation) or a concave curvature (also referred to in the art as a positive-curved orientation). Methods for producing the rolling bar effect are disclosed, for example, in EP 2263806 a1, EP 1674282B 1, EP 2263807 a1, WO 2004/007095 a2 and WO 2012/104098 a 1. An optical effect known as the moving ring effect may also be produced. The moving ring effect consists of an optical ghost image of an object (such as a funnel, cone, bowl, circle, ellipse, and hemisphere) that appears to move in any x-y direction depending on the angle of inclination of the optical effect layer. Methods for producing the moving ring effect are disclosed, for example, in EP 1710756a1, US 8,343,615, EP 2306222 a1, EP 2325677 a2, WO 2011/092502 a2 and US 2013/084411.

An optical effect known as the louvre effect may be produced. The louvre effect includes portions of the pigment particles having magnetic axes parallel to each other and to a plane, wherein the plane is not parallel to the identity document substrate. In particular, the optical effect in which the pigment particles are parallel to each other and have a positive angle of elevation of the plane of the pigment particles relative to the plane of the substrate to which the pigment particles are applied. The louvre effect includes pigment particles as follows: these pigment particles are oriented such that, along a particular viewing direction, they give visibility to the underlying substrate surface, such that indicia or other features present on or in the substrate surface become apparent to an observer, while they hinder visibility along another viewing direction. Methods for producing a louvre effect are disclosed in, for example, US 8,025,952 and EP 1819525B 1.

An optical effect known as a switching effect (also known in the art as a switching effect) can be produced. The flipping effect comprises a first portion and a second portion separated by a transition portion, wherein in the first portion the pigment particles are aligned parallel to a first plane and the pigment particles in the second portion are aligned parallel to a second plane. Methods for generating the flip effect are disclosed, for example, in EP 1819525B1 and EP 1819525B 1. Particularly suitable orientation modes include the louvre effect and the tumble effect described above.

The method for producing the magnetically inductive marking described herein comprises a step c) of hardening the coating composition partially simultaneously with step b) or after step b) to fix the partially reflective, platelet-shaped magnetic or magnetizable pigment particles in a desired pattern in the position and orientation in which they are employed to form the magnetically inductive marking, thereby transforming the coating composition into the second state. By this fixation, a solid coating or layer is formed. The term "hardening" refers to a process comprising drying or setting, reacting, curing, crosslinking or polymerizing the binder composition in the applied coating composition, which binder composition comprises optionally present crosslinking agent, optionally present polymerization initiator, and optionally present further additives in such a way that a substantially solid material is formed which adheres to the substrate surface. As described herein, the hardening step may be performed by using different means or processes depending on the materials included in the coating composition that also include partially reflective flake-like magnetic or magnetizable pigment particles. The hardening step may generally be any step that increases the viscosity of the coating composition such that a substantially solid material is formed that adheres to the support surface. The hardening step may involve a physical process based on evaporation of volatile compositions (such as solvents, etc.), and/or evaporation of water (i.e., physical drying). Here, hot air, infrared rays, or a combination of hot air and infrared rays may be used. Alternatively, the hardening process may comprise a chemical reaction, such as curing, polymerizing or crosslinking the binder and optionally the initiator compound and/or optionally the crosslinking compound comprised in the coating composition. Such chemical reaction may be initiated by heat or IR radiation as outlined above for the physical hardening process, but may preferably include initiating chemical reaction by radiation mechanisms including, but not limited to, ultraviolet-visible radiation curing (hereinafter UV-Vis curing) and electron beam radiation curing (E-beam curing); oxidative polymerization (oxidative reticulation, generally initiated by the combined action of oxygen and one or more catalysts, preferably selected from the group consisting of cobalt-containing catalysts, vanadium-containing catalysts, zirconium-containing catalysts, bismuth-containing catalysts and manganese-containing catalysts); carrying out crosslinking reaction; or any combination thereof. Radiation curing is particularly preferred, and UV-Vis light radiation curing is even more preferred, as these techniques advantageously result in a very fast curing process and thus significantly reduce the preparation time of any document or article comprising the magnetically induced marking described herein. In addition, radiation curing has the advantage of producing an almost instantaneous increase in the viscosity of the coating composition after exposure to the curing radiation, thus minimizing any further movement of the particles. Thus, any loss of information after the magnetic orientation step can be substantially avoided. It is particularly preferred that the radiation curing is carried out by photopolymerization under the influence of actinic light having a wavelength component in the UV or blue part of the electromagnetic spectrum (typically 200nm to 650 nm; more preferably 200nm to 420 nm). The apparatus for UV-visible-curing may comprise a high power Light Emitting Diode (LED) lamp, or an arc discharge lamp, such as a Medium Pressure Mercury Arc (MPMA) or metal vapor arc lamp, as the source of actinic radiation.

As disclosed in WO 2017211450 a1 or US 2017242263, a micro mirror arrangement embossed on a metal substrate or film to produce angle dependent reflective pixels produces an angularly varying image according to the perspective viewing angle. These security features may produce local angle-dependent reflections, but they differ by the fact that they do not disappear completely for any viewing angle. A further difference lies in the fact that: micro mirror structures can be produced at high resolution (30-50 micron pitch) to produce fine images. An implementation that produces a relatively large angle-dependent reflective region may be produced with such a structure that is authenticable using the method disclosed in the present invention. However, these features can be distinguished from magnetically induced markers comprising oriented partially flake-like magnetic or magnetizable pigment particles by spatial variation or entropy in the image, which is higher for magnetically induced markers than for micro mirror based markers.

The arrangement of the microlenses in the array with the mask over the reflective pattern can also produce an angularly dependent varying image or local reflection (such as those described in US 2007273143(a 1)). By properly designing the position of the mask, the microlenses, and the reflective layer behind the mask, an acute angle reflective pattern can also be obtained that can potentially be authenticated using the methods disclosed in the present invention.

Diffractive structures such as holographic foils or embossed diffractive structures may also potentially produce such an angular dependence, but with angularly varying colours, which is distinguished from the previous examples. In WO 2015193152 a1 and US 2016378061 a1, such features are described together with an authentication method using a smartphone camera at two angular positions.

In order to better understand the general concept of the present invention and to point out certain preferred modifications of the general concept, the authentication of a marking comprising partially reflective plate-like magnetic or magnetizable pigment particles with a portable device will be discussed in further detail.

The method of the invention for authenticating a magnetically inductive marker 1 applied on a substrate 2 via a portable device 3 is based on a specific geometrical arrangement of an imager 4 (e.g. a smartphone camera) and a light source 5 (i.e. an LED flash). On most models of smart phones, the camera aperture and the LED flash are positioned side by side with a separation of less than 15 mm. Thus, for a specific magnetic orientation of the flake-like magnetic or magnetizable pigment particles 6 in the marking 1 with respect to the viewing direction, in combination with a suitable imaging distance, the geometrical condition of the light emitted by the flash lamp is fulfilled, i.e. the radiation 7 is reflected back to the camera, i.e. the reflection 8, while for other orientations the reflection is not directed towards the camera. This is shown in fig. 1.

For example, if a magnetically inductive marker has a majority of the flake-like magnetic or magnetizable pigment particles magnetically oriented at 15 ° (angle θ) relative to the normal to the surface, such that incident strobe light is predominantly reflected in that direction, and the marker will glow when illuminated and viewed at an angle of up to the refractive index correction (angle θ) of approximately 15 ° relative to the normal to the surface of the marker. Furthermore, since the angular field of view of the camera 4 is relatively large (typically 30 half angle for samsung S3) and the flash lamp divergence angle is the same, by keeping the smartphone body parallel to the substrate 2, the desired angular orientation of the flake-like magnetic or magnetizable pigment particles relative to the camera to capture reflections can still be achieved, as shown in fig. 2. The smartphone 3 is moved parallel to the substrate 2 at a given distance L, where L is 80mm, for example, while acquiring a set of images or video sequences for authentication. Alternatively, the magnetically inductive tag 1 is also moved in a parallel plane relative to the smartphone 3.

FIG. 3 shows the positions x of magnetic induction markers in a set of images at a respective viewing angle θ for a known smartphone-to-sample distance L₁’…x_n', and a graphical representation of the lens 4' of the camera 4 with an effective focal length f and a graphical representation of the intensity distribution of the magnetically induced marks, wherein I₁…I_nIs the average intensity at the corresponding viewing angle theta.

Fig. 4 shows the intensity and relative intensity distribution of magnetic induction markers extracted from a sequence of images. The first graph shows an uncorrected intensity distribution of the magnetically induced mark regions (which still exhibits an effect). The intensity variation of the Background (BKG) area in the second graph shows a seemingly random phone auto-adjustment. The third graph shows the corrected relative intensity distribution of the magnetically induced marks (which reveals the position dependent reflectivity of the marks).

Specifically, authentication is performed by: calculating for each digital image a respective average intensity I of light reflected by the partially reflective platy magnetic or magnetizable pigment particles and collected by the imager at a respective viewing angle θ;

-storing the calculated average intensity of the reflected light and the corresponding viewing angle to obtain a reflected light intensity curve I (θ);

-comparing the stored reflected light intensity curve I (θ) with the stored reference reflected light intensity curve I (θ) for the mark_ref(theta) are compared, and

-determining whether the magnetic induction marking is authentic based on the result of the comparison.

In one proposed embodiment of the invention, the magnetically induced markers are designed to exhibit one or more distinct regions, each region having a specific orientation of the plate-like magnetic or magnetizable pigment particles. For example, the flake-like magnetic or magnetizable pigment particles are oriented at 15 ° to the W-direction of the first zone and the particles are oriented at 15 ° to the E-direction.

Fig. 5 schematically shows a magnetically inductive label 1 with partially reflective plate-like magnetic or magnetizable pigment particles 6 and 6' magnetically oriented in two opposite directions. Some particles are tilted westward and some particles are tilted eastward, thus reflecting incident light in different directions.

Examples of such magnetically induced markings 1 are shown in fig. 6 and 7, fig. 6 showing a marking comprising plate-like magnetic or magnetizable pigment particles 6 (petals) and particles 6 '(disc), and fig. 7 showing a marking comprising particles 6 (outer petals) and particles 6' (inner petals). In this way, reflections from the particles of the first zone may be obtained by placing the marker at the right end of the field of view of the smartphone, while reflections from the other zone may be obtained by placing the marker at the left end of the field of view of the smartphone. This is further illustrated in fig. 8, where fig. 8 illustrates smartphone locations and corresponding images obtained in those locations.

In another embodiment of the invention, instead of moving the smartphone in a linear direction parallel to the tag, a 90 ° rotation of the tag itself, also parallel to its plane, may be made. Fig. 9 is a schematic illustration of the effect of a 90 ° rotation of the marker or smartphone in the plane of the marker 1 on the substrate 2 and the guide target 9 on the screen. On the left image, the central circle 10 is highly reflective compared to the rest of the mark. On the right image, the central circle 10 is not reflective compared to the rest of the marker and resembles the background.

This is explained by the fact that: in one orientation, the partially reflective flake-like magnetic or magnetizable pigment particles emit light, while in a 90 ° rotational orientation they do not emit light, which serves as an authentication criterion.

Another embodiment of the invention may utilize a smartphone to rotate at 90 ° while keeping it parallel to the marker instead of rotating the marker itself. In this case, the first or second region of the mark will reflect that it can be used for authentication.

The exact position of the marker on the picture preview of the smartphone together with the distance of the smartphone to the marker precisely defines the angle at which reflection can be obtained from the plate-like magnetic or magnetizable pigment particles. By providing the guide target 9 on the smartphone screen preview, the user can easily position the smartphone laterally at a precise position, so that a precise angle can be obtained when also controlling the viewing distance.

The longitudinal position (viewing distance) may be guided by the size of the target that should fit the size of the mark at the correct distance, or by simultaneously aiming at a second target of a second mark or barcode printed in addition to the magnetically oriented design, or by a written message on the screen specifying that the user is moving closer or farther.

This makes the authentication method highly sensitive to the precise flake-like magnetic or magnetizable pigment particle angle and thus allows good discrimination of potential mimics that will not reproduce a precise orientation.

Fig. 10 is a schematic representation of a label with partially reflective plate-like magnetic or magnetizable pigment particles 6 having a magnetic orientation in the E-direction and another type of particles 6' oriented in the S-direction of 90 ° relative to the particles 6. In a similar manner to the previous embodiments, the sequence of images may be recorded during rotation of the marker relative to the smartphone.

Authentication is performed by analyzing the reflected intensity on the first and second regions of the marker in two images acquired at two precise locations of the smartphone, confirming the orientation angle. Furthermore, the sequence of images may be acquired during movement of the smartphone between two positions in a direction parallel to the planar layer of the marker. The intensities from two different regions with flaky magnetic or magnetizable pigment particles oriented in either direction are then extracted and recorded as a function of position. Two intensity distributions are obtained which can be analyzed in a similar manner as described in fig. 11 and/or fig. 12 and 13.

In this regard, fig. 11 shows a graphical representation of the intensity distribution, its first and second derivatives, with respect to position. The first derivative magnitude provides the rate of change of intensity and the zero position gives the position of the intensity maximum. The second derivative shows that the intensity distribution has two inflection points (inversions).

Fig. 12 provides a graphical representation of the intensity cross section of the marker at one specific position relative to the smartphone, showing individual flake-like magnetic or magnetizable pigment particle reflections and high variance of intensity.

Fig. 13 shows the distribution of relative intensity and intensity variance as a function of the position of the magnetically sensitive markers in the image set, which shows similar behavior of the relative intensity and variance.

In a similar embodiment, the video sequence may be acquired during controlled lateral movement of the smartphone in a plane parallel to the markers. The movement may be guided by augmented reality, where the moving target is displayed on a smartphone display, and the user is encouraged to move the phone while keeping the marker within the target. In this way, the rate of change of intensity with magnetically oriented glitter flake-like magnetic or magnetizable pigment particles as a function of viewing angle (calculated from the position of the marker on the picture of the smartphone and the distance of the smartphone to the marker) can be extracted from the video sequence. This rate of strength change is a strong authentication parameter because it is very sensitive to the precise angle of orientation of the flake-like magnetic or magnetizable pigment particles. The rate of change of intensity can be obtained from the first derivative of the distribution as shown in fig. 11. The second derivative can also be used as a strong authentication parameter by allowing the location of the inflection point in the distribution to be determined. State of the art magnetic orientation may provide for angular position of the flake-like magnetic or magnetizable pigment particles down to within +/-2 degrees. Even if a counterfeiter can produce a marking with oriented flake-like magnetic or magnetizable pigment particles, it is not possible to obtain a precise orientation angle and a counterfeit marking can then be detected as counterfeit by this method with high accuracy.

It is also possible to use the video sequence to obtain the relative intensity as a function of the illumination angle of the marker (which corresponds to the position of the marker on the screen during controlled lateral movement of the phone) and furthermore to obtain the variance of the pixel intensity within the marker. These two distributions of relative intensity and variance depend on the orientation of the plate-like magnetic or magnetizable pigment particles in the magnetically inductive marker. Fig. 14 and 15 show examples of relative intensity distributions and variance distributions of different markers. Examples include marks with inks containing non-oriented and non-magnetized flake-like magnetic or magnetizable pigment particles, magnetically induced marks, and finally marks with holograms and micro mirrors as described above. In fig. 15, the left graph shows the relative intensity distribution (average intensity of the viewed security mark relative to the average intensity of, for example, a reference paper region), and the right graph shows the distribution of the variance of the intensity over the pixels of the image comprising the mark.

It can be seen that the marks with non-oriented flake-like magnetic or magnetizable pigment particles have a centered and symmetrical relative intensity distribution as well as a variance distribution. In contrast to these examples, the magnetic induction markers described herein show a distribution with strong skew. The intensity and variance peaks are shifted to one side of the picture due to the orientation of the flake-like magnetic or magnetizable pigment particles contained in the security ink. The example with the hologram shows a significant difference in the peak positions of the distribution of the three color channels, which is not the case for any magnetically induced mark. Finally, micro-mirror based markers differ from magnetic induction markers by very low variance and non-peak high intensity, even though the peak position may be similar to that of the MOI markers.

This shows that the proposed method allows to accurately distinguish different types of angle-dependent markers and even to infer the orientation angle of the plate-like magnetic or magnetizable pigment particles or the embossed structures or micro mirrors. This is a clear demonstration of the advantage over the methods described in the prior art where the images are captured at only two angular positions.

The measurement shown in fig. 15 was made with a camera fixed at 80mm from the smartphone samsung S3 parallel to the sample of interest of the smartphone mobile within the field of view of the smartphone. The camera is set to macro auto focus, fixed white balance, ISO settings, and manually takes a sequence of pictures for the example. The video sequence may be used with a function that uses an object tracking function to adjust the focus and exposure of an object of interest.

The individual areas (blocks) that are found to be of interest with respect to the QR code or other suitable geometric marker on the tag, the areas (blocks) with the security marker referred to as signal areas (blocks) or the paper areas (blocks) referred to as background areas (or background blocks). Calculating the location of the signal and background regions (tiles) on the smartphone screen includes calculating the center and area with the pixels that contain these regions (tiles). The mean intensity and variance of all pixels within a region (patch) are calculated for all color channels (e.g., R, G or B).

The relative intensities of the respective positions of the signal and background regions (patches) are calculated using the ratio of the average pixel intensity in the signal region (patch) to the average pixel intensity in the background region (patch), and this is done for all color channels. The average pixel intensity of the background area (patch) is always calculated for the color channel with the maximum intensity of the background area (patch) to ensure that the reference is the signal form channel with the maximum reflectance using paper.

Using the reference to calculate the relative intensity makes it possible to use a smartphone camera with automatic setting of the exposure time.

Further embodiments may include classifier-based or neural network-based machine learning authentication algorithms that are capable of distinguishing true intensity distributions (or other measured or extracted features, such as variance distributions or image entropy, etc.) from unreal intensity distributions.

As an example, authentication of the token may be accomplished using machine learning. This operation then comprises the following three steps: feature extraction, model training and selection, and prediction.

With respect to the step of feature extraction, the imager returns a series of RGB images I (θ), where θ_min≤θ≤θ_maxIs the scan angle relative to the normal of the mark. If necessary, only the region of interest (RoI) around the mark can be saved by cropping the image. These images may be linearized and converted to gray levels (e.g., r.c. gonzalez, t.e. woods, "Digital Image Processing," Fourth Edition, Pearsons, 201)7, described above). However, separate processing of the color channels is also possible.

For each image, one or more metric functions f (θ) are calculated. A detailed description of image metrics applied to images can be found in the above-mentioned book by r.c. gonzales and t.e. woods. The metric may be computed directly on the image intensity or on a transform such as the Discrete Fourier Transform (DFT) or Discrete Wavelet Transform (DWT). Among the useful metrics that can be used, we find the mean, standard deviation, and entropy. Depending on the metric used, we may need to scale it with the average intensity of the reference neighboring RoI (this operation allows to compensate for the variable exposure time of the imager and any variation in the illumination of the marker).

In order for all measurements to have the same scale, the metric must be estimated on a uniform sampling grid of angles. These angles must be symmetrical about the normal to the sample, e.g., θ [ -20 °, -18 °, …,0, …, +18 °, +20 °]. We can represent this uniform grid as θ ═ θ₀ θ₁ … θ_D-1]Where D is the number of angles. Here, D is 21, for example. In practice, scanning at evenly spaced angles may not always be possible, and interpolation of the metrics may be necessary. At the end of the scanning process, we obtain a feature vector x^T＝[f(θ₀) f(θ₁) … f(θ_D-1)]＝[x₀ x₁ … x_D-1]. By further scanning the different markers N times to take into account their variability, we build a data set X with size D × N^T＝[x₀ … x_N-1]。

With respect to the steps of model training and selection, general Machine Learning techniques for classification and detection are described in c.m. bishop, "Pattern Recognition and Machine Learning," Springer, 2009. Here, the authentication problem is reduced to distinguish between a true feature vector and a false or attack feature vector. However, while the true feature vector is known and available, other feature vectors are unknown or rare. Thus, it is not feasible to directly train both classes of classifiers. Certifications may be shown to be equivalent to a Class of classifications as described in o.maze, "One-Class classes: a Review and Analysis of reliability in the Context of Mobile-Masquerader Detection," South African Computer Journal (column 36, pages 29-48, 2006). In this scenario, the classifier models rely only on the true feature vectors to learn their parameters and decision boundaries. Among them, Support Vector Data Description (SVDD), v-support vector classification (v-SVC), Gaussian Mixture Model (GMM), and deep learning models (such as an auto-encoder, etc.) are of practical interest. The choice of model is dictated by its performance during training and is also constrained by its complexity. At equivalent performance, a simpler model is preferred.

Prior to training the model, the data set X is preprocessed as shown in the following figure and the following steps are performed:

-sample removal. Defective samples (such as saturated or samples with missing features, etc.) are discarded.

-sample normalization. The feature vector is normalized to unit energy.

-feature normalization. Characteristic mean value mu (theta)_d) And characteristic standard deviation σ (θ)_d) Are estimated and removed feature by feature.

-sample castration. The low-order polynomial trend of a fixed order p is estimated and removed for each sample.

-feature reduction. Inter-feature correlations are removed and the dimensionality of the problem is reduced. Here, the reduction may be from D21 to K3 to 5, for example. Lower dimensionality optimization problems converge faster and allow easier inspection. This step is accomplished by Principal Component Analysis (PCA) (see book c.m. bishop, "Pattern Recognition and Machine Learning," Springer,2009), which yields a vector subspace V ═ with size D × K₀ … v_K-1]. After PCA, we project the dataset X onto the subspace V, which results in a reduced feature dataset X 'with size K N'^T＝[x′₀ … x′_N-1]. This data set is used to learn the parameters Θ of a candidate class of classification models. Finally, the best candidate is retained for prediction.

Regarding the prediction step, it performs operations of data cleaning, sample normalization, feature normalization, castration, subspace projection, calculation of model decision functions on the data set. Finally, after feature reduction by subspace projection, the decision function of the classifier with Learning parameters is calculated (see also i.goodfellow, y.bengio, a.courville, "Deep Learning", MIT Press, 2016).

Still further embodiments may include perspective correction to correct for imperfect or varying alignment of the imager with the marker plane. In addition, spatial distribution stretching or compression due to camera-to-marker distance variations can also be corrected by extracting the dimensions of the reference marker outline or barcode in the image.

Fig. 16 shows different embodiments of a magnetically inductive marker: a) an oriented pattern in which all the pigment particles are co-parallel (referred to as the louvre effect described above); b) "rolling bar effect" in which the angle of the pigment particles increases from the center of the mark to the edge; c) "flip effect" in which one region of the mark has partially reflective flake-like magnetic or magnetizable pigment particles that are co-parallel at one angle and another portion of the mark has pigment particles that are co-parallel at a different angle; d) "hiding and revealing" (referred to as the louvre effect described above), wherein a background image or design is printed under magnetically induced indicia and is hidden by plate-like magnetic or magnetizable pigment particles for a given viewing angle or revealed for another viewing angle; e) superimposed "flip effect", in which two different designs with co-parallel platelet-shaped magnetic or magnetizable pigment particles are superimposed; f) a "rotating" pattern in which two regions (each having co-parallel platelet-shaped magnetic or magnetizable pigment particles) have an orientation that is tilted 90 ° to each other.

In an embodiment, a geometric reference pattern in the form of a coded mark (such as a coded alphanumeric data, a one-dimensional barcode, a two-dimensional barcode, a QR code, or a data matrix) may at least partially overlap the magnetically induced mark. Furthermore, this allows for example to identify the markers for traceability purposes.

Fig. 17 shows exemplary various marker designs in which the magnetically inductive marker 1 is integrated with the QR code 12 within a background area (background block) 13, wherein the magnetically inductive marker 1 is close to the QR code 12, or wherein the magnetically inductive marker 1 is located inside the QR code 12, or wherein the magnetically inductive marker 1 is located above the static QR code 12. The QR code 12 may be static or dynamic (different for each tag 1), depending on the application. The QR code 12 is used to effectively locate the marker and determine the magnification and allow the position in the field of view of the magnetically induced marker to be extracted during the sliding movement of the smartphone.

In this case, the QR code 12 is read at a location where the magnetically induced markers do not reflect to have sufficient contrast that is not altered by the magnetically induced marker return reflections, and the magnetically induced marker distribution is measured and analyzed on a black module of the QR code to have maximum contrast between locations where the flaky magnetic or magnetizable pigment particles are oriented to reflect back or not.

Preferably, the relative intensity of the magnetically induced markers can be measured from images that are part of the video sequence using the following method:

-determining the center of a reference pattern (symbol) in an image with index i;

-calculating the position of the magnetically sensitive mark region relative to a reference pattern (symbol);

measuring the average intensity I of the magnetically induced mark region_iThe average intensity is defined as the average value of the intensities of all pixels in the magnetic induction mark area;

-calculating the position of a reflectivity reference region, called background region-BKG region;

measuring the average intensity I of the BKG region_BKGi；

-calculating the relative intensity I of the magnetic induction marking zone for all n images from the video indexed I1.. n_i＝I_i/I_{BKG i}。

Measuring the relative magnetic induction marking block intensity using a geometric reference pattern (i.e., QR code quiet zone) placed near the magnetic induction marking zone with a pre-known reflectivity may further reduce the sensitivity to variable ambient illumination.

The present invention provides an improved, accurate and reliable solution that is robust against ambient light disturbances, does not rely on high resolution printing or on complex movements of the smartphone, and avoids difficult to control and non-intuitive tilting or azimuthal or rotational movements.

In fact, the invention allows easy control of the movement (i.e. parallel to the substrate) with good immunity to ambient light variability due to the light source (preferably a smartphone flash), which dominates the ambient light under most conditions. Operating at close range with a smartphone positioned parallel to the substrate further reduces external light contamination by obscuring the area of interest. The control for keeping the phone in a given plane can be easily achieved by using a gyroscope, e.g. a smart phone. It may also be measured by the size in the image and the geometric deformation (e.g., perspective) of the label, marker or QR code being viewed. This is a key advantage of the present invention and is a substantial improvement over the prior art.

Thus, the present invention does not rely on high resolution printing nor on the complex movements of the smartphone, and utilizes a smartphone internal LED flash, which increases its immunity to external (ambient) light conditions. Furthermore, due to the precise and low variance orientation of the flake-like magnetic or magnetizable pigment particles (below +/-2 °), the present invention is highly discriminative for simulations and selective for other angle-dependent reflective markers.

Another advantage of the present invention over the prior art is provided by the detailed information obtained from the intensity distribution, which provides an enhanced level of security in authentication. For example, the rate of strength change increases and decreases are directly related to the uniformity of the orientation of the flake-like magnetic or magnetizable pigment particles, which is one of the most challenging features obtained during the printing process and therefore the most difficult to forge. Furthermore, the angle at which the flake-like magnetic or magnetizable pigment particles are oriented can be inferred from the angular reflection distribution, provided that a scale reference (such as a QR code or a machine-readable code of any known dimension) is present in the image and the parameters of the camera are well known for calculating the viewing angle.

The above-disclosed subject matter is to be considered illustrative, and not restrictive, and is intended to provide a better understanding of the invention as defined by the independent claims.