DE102011075943A1 - Method and device for verification of security documents by means of white light interferometry - Google Patents

Abstract

The invention relates to a verification device and a verification method. The verification method comprises the steps of: orienting the security document (13) relative to a white light interferometer (2), performing a white light interferometric examination at at least one location (P1-P3) of an examination surface (15), with a depth profile along an examination direction (19-1 to 19-3), derive a feature from the depth profile and compare the at least one derived feature with one or more specifications in order to derive a verification decision.

Description

The invention relates to a method for the verification of security documents and to a verification device for security documents which carry out a white light interferometry and use it to verify existing security features in a security document.

A variety of features are known in the art that are used to secure documents that they can not be unauthorized, falsified or manipulated. Security features may thus be all features that make duplication, unauthorized production, tampering or other manipulation of a document or item difficult, impossible, or at least make a precise examination of these undesirable actions verifiable.

Security documents are all documents that have at least one feature that make duplicating, copying, falsifying or other manipulation difficult or impossible. Security documents include, for example, passports, identity cards, driving licenses, access cards, visas, but also labels for high-quality products, such as software, tickets, but also bank cards, credit cards, phone cards or the like, as well as documents that embody a value, such as stocks, securities, banknotes, Postage stamps, customs stamps and others, just to name a few examples.

As security features, a wide variety of features can be used. For example, the material composition of a document can serve as a security feature. By way of example, reference should be made here to security papers, as used for example in ID or banknote printing. Also, the different printing methods, which are hard to imitate or reproducible in part or in combination for a counterfeiter or manipulator can serve as security features. In the production of security documents, almost all current printing processes, such as intaglio printing, high-pressure processes, but also inkjet printing processes or offset printing processes, are used in their different forms. These usually show a typical characteristic printed image, which can be distinguished from the printed images produced by other printing processes, at least in a microscopic examination.

Other security features include diffractive structures, relief structures, special colors and the like. Particularly in modern security documents which comprise a document body made of one or more plastic materials, a plurality of different security features can be integrated into a security document. However, with advances in technology that allow for the incorporation of novel and more complex security features that are harder to falsify, especially in mass-produced security documents such as banknotes or identity papers, counterfeiters' ability to mimic and / or distort security elements also increases. Therefore, it is necessary to provide more sophisticated methods and apparatus for verifying security features that allow a reliable distinction between genuine security documents and counterfeit security documents. Such a procedure is called verification.

Different verification methods and verification devices are known from the prior art, which are usually adapted to special security features and provided for their verification. It is desirable to provide new verification methods and verification devices that can be used for a variety of security features and / or security documents to verify their authenticity and authenticity.

The technical problem is solved by a verification method which uses a white light interferometry to non-destructively examine a surface structure as well as an internal structure of documents. Verification can be carried out with a verification device comprising a white light interferometer, which is designed to create a depth profile of the security document at least at one point. This does not necessarily extend over an entire extent along a direction of examination of the security document. This means that a depth profile does not have to penetrate the entire document. This is not possible, for example, with documents comprising opaque layers or metallically reflecting layers by means of white-light interferometry.

Following this basic idea, a method is provided for verifying a security document comprising the steps of orienting the security document relative to a white light interferometer, performing a white light interferometric study on at least one location of an examination surface of the security document, creating a depth profile along an examination direction which is oriented transversely to the examination surface is, and deriving one Feature from the depth profile and comparing the at least one derived feature with one or more constraints to derive a verification decision.

Such a method can be implemented with a verification device which comprises a document holder and a white light interferometer which is designed to create a depth profile along at least one position on a surface of a security document arranged on or in the document holder along an examination direction oriented transversely to the surface. and further comprises an evaluation device which evaluates the at least one depth profile.

definitions

As a white light interferometer, any optical interferometric device is considered, which brings broadband light with spatial coherence to the interference and evaluates this interference. It is irrelevant whether this light spectrum in the visible wavelength range, infrared wavelength range or UV wavelength range is arranged wholly or partly.

As a depth profile, measurements of a physical quantity associated with different depths along an examination direction are considered, the examination direction being in an interior, i. the volume of a body, such as a document, extends. As a rule, a depth profile begins outside or on the surface of the object into which the examination direction or distance extends. A depth profile is associated with a position on a surface of the examined object, for example a security document. The position is that on the surface where a straight line indicating the direction of the examination intersects the surface.

Depth values are the distances along an examination direction, along which a depth profile is created, based on a reference value. As a reference value, the intersection of a straight line indicating the examination direction with the surface of the document support or any other surface perpendicular to the light propagation direction in the measuring arm.

The examination direction is the direction along which the light impinges on the surface of the object to be examined. In doing so, local unevennesses of the surface are disregarded.

The measurement information derived from the interference values associated with a depth value is referred to as the intensity value.

By deriving a feature is meant deriving a quantity or any abstract or mathematical object or construct, for example a vector of intensity values, or a group of depth value intensity value tuples. The set of depth values and intensity values, or a selection thereof, as well as a value resulting from a statistical evaluation represents a derivative of a feature.

An intensity value change is a value assigned to a depth value of a depth profile and which is determined by comparison with one or more intensity values corresponding to spatial regions of the object being examined that are adjacent to the region defined by the position and the depth value (and for all collectively acquired depth profiles uniform examination direction) is defined. In the simplest embodiment, the intensity value change is determined by a comparison with the intensity value given for the neighboring depth value or the neighboring depth values in the same depth profile. In other embodiments, the intensity values of adjacent surface positions and equal or adjacent depth values may also be taken into account.

Preferred embodiments

The invention according to its basic idea offers the advantage that structures occurring on the surface or in the interior of a security document, which can occur at different depths of the document transversely to the surface, can be verified. For example, it can be determined in which plane of a document body made of transparent plastic material a piece of information perceptible as blackening for a human viewer is stored. In this case, different methods by which the information can be stored in the document body differ with respect to the spatial design of the components of the security document carrying the information. If the information is printed, for example, on a substrate layer which is subsequently laminated with further substrate layers to form a document body, the information is located in the vicinity of an at least originally existing layer boundary. On the other hand, if the information is introduced via a laser marking process, a larger volume range is usually inked via a partial carbonization of the plastic material. In the depth profile can be seen at what depth the information is marked, so that a printing process can be distinguished from a laser marking process. Laser marking processes are sometimes referred to as laser engraving.

In order, in particular, for security documents which have a transparent or partially transparent document body which is made of plastic, to minimize the possible diffraction effects on the document surface, the security document is preferably oriented such that the examination direction determined by the white light of the white light interferometer striking the security document is oriented perpendicular to a surface of the security document. The surface here is the examination surface, which is usually the surface of the security document, which has the largest areal extent. In a verification device, such an orientation can be achieved simply by configuring the document receiver in such a way that a security document placed thereon or in it is automatically oriented with its surface perpendicular to the examination direction. For example, the document receptacle can be configured as a support surface, which is formed, for example, by a transparent, plane-parallel plate having almost no absorption in the wavelength range, onto which the security document is laid flat or pressed flat with its surface to be examined. Pressing ensures that the security document fits optimally against the support surface along its entire or a larger portion of its surface. This is particularly advantageous for security documents which are deformed in use.

In a preferred embodiment, a white light interferometer comprises a light source, a beam splitter, a detector, a reflector mounted on a controllable linear actuator, and a control and data acquisition device, wherein the light source produces broadband, spatially coherent light and is positioned relative to the beam splitter the beam splitter directs a portion of the light into a measuring arm in which the object receptacle is located and directs a portion of the light into a reference arm in which the reflector is arranged to reflect the light back onto the beam splitter and superimpose it with the light which is reflected back to the beam splitter on a security document placed in or on the document receiver, the detector being arranged to be formed by the superposition of the reflected light of the reference arm with the reflected light of the measuring arm Interference signal, wherein the control and detection means is coupled to the linear actuator to vary during the detection of the interference signal, a reference arm length over a linear displacement of the reflector, the reference arm lengths corresponding to Messarmlängen corresponding distances from the beam splitter along the examination direction which correspond at least to the surface of the security document on and in the document recording or into the interior of the document recording. The variation of the reflector position thus varies a reference arm length of the interferometer. The light in the measuring arm hits the surface of the object to be examined, i. of the security document, and also penetrates at least partially into the security document. Depending on the nature of the security document or features contained therein, portions of the examination light in the measuring arm are reflected back into the interferometer both on the surface and along the propagation path of the light along the examination direction in the security document. Depending on the reference arm length, which is determined by the position of the reflector (for example a reference mirror), it is determined which portions of the light which are reflected back into the interferometer along the examination direction in the security document lead to constructive interference at the detector. The reflector position in the reference arm thus determines the depth, which is scanned by the resulting interference. However, since monochromatic light is not used, but rather broadband, spatial coherence light is used, the resulting interference pattern is much more complex. However, computational algorithms are known from the prior art which make it possible to derive a depth profile along the examination direction from the temporally successively obtained interference signals which are detected during the variation of the reference arm length. Such algorithms are also used in optical coherence tomography (OCT). Optical coherence tomography (OTC) is known in particular from the field of ophthalmology and is used there, for example, to examine the retina.

The white light interferometer is thus preferably designed as an optical coherence tomograph.

Much more accurate information or more complex verification is possible when depth profiles are determined for multiple locations on the surface of the security document. In a preferred embodiment, multiple locations that are co-located along a path on the surface of the security document or multiple locations located in a surface area of the security document surface that includes the at least one location coincide with the depth profile for the at least one location recorded depth profiles. In a suitable embodiment, it is possible to achieve that a light beam of the light beam expanded along one direction broadband, a spatial coherence having light is sent to the beam splitter and the security document along a line, ie a distance, illuminated on the surface of the security document and thus transversely to the surface, preferably perpendicular to the surface, at the illuminated locations in each case a depth profile is detected simultaneously , For this purpose, it is necessary for the detector for each of the locations to be detected to comprise a light-sensitive detection element in order to be able to detect the interferences assigned to the individual locations and to be able to derive the corresponding depth profiles for the individual locations. If the light is widened along two spatial directions, it is possible to record the depth profiles simultaneously for locations in a surface. In this case, the detector must have not only a linear array of photosensitive sensors, but a flat array of photosensitive detection elements, which can detect the interference signal during the variation of the reflector position for the respective locations in the area.

In order to be able to carry out a verification, it is advantageous if at least one cross-sectional area of the security document determined from the acquired depth profiles is displayed on the display device, which is spanned by the examination direction and the path or a contour lying in the area region. In principle, it is possible to form the one axis of the cross-sectional area by any arrangement of positions on the surface of the security document and to arrange the corresponding depth profiles next to each other to form a cross-sectional area. In general, however, it makes sense that the depth profiles shown side by side in the cross-sectional area also correspond to points which are arranged spatially adjacent to one another on the surface. An advantage of such a cross-sectional area representation, which, for example, along a path represents a cross-section through a volume area in the interior of the document transversely to the surface of the document, is that, for example, existing layers or layer transitions are recognizable in the document. Modern security documents are often assembled from multiple substrate layers in a lamination process. It is not always possible to carry out this lamination process in such a way that a monolithic document body exists in which the original layer boundaries in the solid body can no longer be detected by measurement as phase transitions.

In the case of security documents in which such a monolithic design is not successful in the document body, these layer boundaries, which are not perceptible to a human user in an optical viewing, can nevertheless be detected by different intensity values in the depth profiles. Such a cross-sectional area thus shows intensity values or intensity value changes deviating from the layer boundaries, so that these layer boundaries are clearly recognizable in the cross-sectional representation. If such a document has now been split for a manipulation in order, for example, to modify passport information or other information identifying, for example, a person to whom the security document is assigned, after a reassembly of the split layers, clear deviations in the layer structure are generally evident , which is visible in the weilichtinterferometrisch derived cross-sectional area to recognize. Visual inspection of such cross-sectional representation thus allows verification personnel to easily locate documents that have been manipulated. Similarly, different printing methods can be recognized. If, for example, a high-pressure method is used, bruising occurring in the printing plane during printing can be recognized at the edge of the embossed letters or characters. A printing layer produced by high pressure thus shows characteristic height profile properties that can be derived from the cross-sectional profile. The same applies to printing elements produced by intaglio printing.

For example, in modern security documents made of plastic, ink-jet printing methods are used whose ink is made on the basis of the plastic material from which the substrate layers to which the inkjet printing is applied are made. These printed layers have the advantage that they can also be executed over a large area without thereby creating a delamination possibility on the printed surface, since the ink material optimally combines with that of the adjacent substrate layers during the lamination step. However, the colorants used do not necessarily remain on the printed surface, depending on the specific composition of the printing ink used, but optionally diffuse specifically into the substrate layer to which the print is applied. In an investigation of the depth profile, pressure ranges generated by means of such an ink jet printing method can thus be clearly differentiated from other pressure ranges.

Also, other manipulations associated with intermittent cleavage or delamination of a document body, and / or optionally planing and / or re-inserting material, inserting altered or corrupted other security elements, such as metallized foils or patches of other types or holograms, in conjunction stand, are with recognizable in the proposed verification method, since the same process parameters that were used in the original document production to connect the different layers to one another are generally not usable during the assembly and / or insertion. Therefore occur at the points where manipulations were made, in the cross-sectional profile clearly perceptible changes, for example in the form of cracks in otherwise parallel layer transitions.

In order to enable a machine evaluation, depth profiles or cross-sectional areas formed from these can be stored as defaults in a database or memory as defaults. By comparing the determined depth profiles, cross-sectional profiles with the specifications, a verification is possible.

In one embodiment, it is provided that the intensity values and / or intensity value changes corresponding to individual depth values or depth ranges are evaluated statistically with regard to the frequency in order to determine a deviation from an expected statistical distribution as an indication of a manipulation or forgery. By way of example, a region adjacent to a layer transition in the document can be selected as the depth region in which no intensity values and / or changes in intensity value characterizing the transition occur in a non-manipulated security document. Since with manipulated security documents the layer transition or associated characteristic intensity values or intensity value changes also occur at depth values which do not correspond exactly to the depth of the layer transition, such values will, for example in a forged security document, indicate intensity values indicating a layer transition with a greater frequency than at Original documents found. It is likewise possible to evaluate the depth range of the layer transition and to find in the region of the layer transition in the case of a manipulated security document an accumulation of intensity values or intensity value changes which do not correspond to a layer transition.

In another embodiment, the depth values at which intensity values or intensity value changes, which are each determined by comparing an intensity value with the intensity value of an adjacent spatial area in the security document or by comparing the intensity value with the intensity values of adjacent spatial positions in the security document, are above a threshold value or occur within a range of values delimited by an upper threshold and a lower threshold, evaluated in frequency to determine deviations and / or reconciliation of one or more expected statistical distributions, and to derive therefrom the verification decision. If, for example, the intensity values which characterize a particular layer transition or are typical of a particular printing process are evaluated in this way, an indication is given of the depths at which these types of transitions or information introduced in this way by printing technology can be found. In a manipulated document, for example, such a depth value distribution for a layer transition is broadened because the layer transition occurs at different depths due to the manipulation.

The various statistical evaluation methods mentioned can also be evaluated and / or used in combination.

In a further embodiment it is provided that the depth values to which intensity values of a value range are assigned in at least one detail, for example a depth value range, or depth values to which intensity value changes of a value range are assigned with respect to their assigned positions along the at least one distance or curve are approximated by a predetermined parameterized function of the position and the verification decision is made on the basis of the parameters derived in the approximation. Are in a security document as a security feature, for example, in a finished document disposed in the interior boundary layer before joining them recesses introduced that modify the surface profile in a sectional plane and then filled so that the finished security document no hollow volumes are included, then results in a suitable choice of Cross-sectional area a characteristic, the contours of the introduced recesses following, corresponding to the boundary edge line. A function can then be adapted to this line, which can optimally approximate this line of intersection. In the prior art, approximation methods are well known which vary the parameters of a function in such a way that the best possible match is achieved between the layer line profile given by the experimentally determined values, in this case the depth values, and the parameterized function. On the basis of the parameters, which then characterize, for example, a position, shape and depth of the recesses introduced, a verification can then be carried out in a simple manner.

For a human perception of the different intensity values, it is advantageous if they are displayed on the display area, for example via different color values. A display device, which is coupled to the evaluation device, on which a cross-sectional area formed by the at least one depth profile and further depth profiles for further positions on the surface of the security document can be displayed, is preferably designed such that it provides such a colored representation. It should be noted that the colors are not correlated with the colors with which the security features may be stored in the security document. They merely serve to make it easier to distinguish between the different intensity values determined.

The invention will be explained in more detail with reference to preferred embodiments with reference to a drawing. Hereby show:

1 a schematic representation of a verification device;

2 a schematic representation of a section of a layer structure of a security document, in which information is introduced by means of an ink-jet printing process;

3a . 3b schematic representations for explaining a security feature, which is formed via an introduced and then filled-in recess;

4 a schematic representation of a derived from depth profiles cross-sectional area for a security document with a structure according to 3b ;

5 a schematic representation of a derived from depth profiles of a security document cross-sectional area, the feature of 3b does not have;

6 a schematic representation of a statistical evaluation for a document with unmodified parallel layers, in which the frequencies of the intensity values of an intensity value range are compared with their associated depth values;

7 Graphical representation of a corresponding statistical analysis analogous to the 6 for a security document with a configuration analogous to that according to 3b ;

8th Presentation of another statistical evaluation of a non-forged security document;

9 a schematic representation of a statistical evaluation analogous to the 8th for a fake security document; and

10 schematic graphical representation of an evaluation in which the depth values of a depth value range are plotted against the assigned positions on the surface and a parameterized function of the position is adapted to the depth values.

In 1 is schematically a verification device 1 shown. This includes a white light interferometer 2 , The white light interferometer 2 includes a light source 3 , which broadband light 4 emitted with spatial coherence. In the illustrated embodiment, the light 4 initially via an optical element 5 widened. This then hits a beam splitter 6 , The beam splitter leaves a part of the light 4r in a reference arm 7 enter, at the end 8th a mirror 9 as a reflector. This is movable on an actuator 10 stored. The actuator 10 can the mirror 9 shift linearly such that a length l _{r of} the reference arm can be varied.

At the beam splitter 6 becomes another part of the light 4m in a measuring arm 11 directed. In the measuring arm 11 is on a trained example as a glass plate document holder 12 a security document 13 arranged as a measuring object. The on the surface 15 and in volume 16 inside the security document 13 in the measuring arm 11 reflected light back 4mR is at the beam splitter 6 with that of the mirror 9 from the reference arm 7 reflected back light 4RR superimposed and on a detector 14 guided. In the illustrated embodiment, the detector 14 a plurality of photosensitive sensor elements (not shown).

As an example, the beam guidance for three positions P1, P2, P3 on a surface 15 of the security document 13 shown. At the surface positions P1, P2, P3 or inside the security document 13 along the propagation directions of the surface 15 incident light 4m of the measuring arm 11 reflected light back 4mR will be with the corresponding in the reference arm 7 reflected back light 4RR on a sensor element of the detector 14 superimposed and recorded as interference signal. During the measurement, the length l _{r of} the reference arm becomes 7 varied. Corresponding measurement lengths l _m of the same length extend from the surface 15 right down to the volume 16 of the security document 13 , The time-resolved detected interference signals are a control and data acquisition device 17 supplied on the basis of the measured values of each measuring element, a depth profile to the corresponding position P1, P2, P3 along examination directions 19-1 to 19-3 determined. The examination directions 19-1 to 19-3 are by the direction of the light 4m determined at the corresponding positions P1 to P3. It is understood that depending on the illumination of the document 13 and a resolution of the detector 14 Depth profiles for more positions along a stretch 20 or, unless the light 4 expanded flat, can be detected and evaluated for distributed over an area positions at the same time. The control and data acquisition device 17 controls the actuator during measurement data acquisition 10 with which the mirror 9 is linearly displaced to vary the reference arm length l _r and hereby the corresponding Meßarmlänge l _m .

The acquired measurement data representing interference signals is provided by the control and data acquisition device 17 evaluated in order to create the corresponding depth profiles for the individual positions P1 to P3. This is done according to algorithms known for optical coherence tomography. A depth profile to a position comprises for the depth values along the examination direction the associated intensity values, which represent a measure of the reflection of the area of the examined security document, which is determined by the position and the corresponding depth value. In an evaluation device 21 then the depth profiles are evaluated. The control and data acquisition device 17 can with the evaluation device 21 be summarized in a facility. Both may be implemented individually or collectively as a program-controlled device. Alternatively, at least the control and detection device 17 purely in hardware. In the illustrated embodiment, the verification device comprises 1 additionally a display device 23 , which is a freely programmable display area 24 includes, on the example, derived from depth profiles cross-sectional area 25 is pictured. This is schematically in 1 shown. You can see different layer boundaries 44 . 45 where significant intensity values occur. In addition, the verification device may include a storage device 26 include in the default data, for example, for certain depth profiles, statistical key figures or exemplary cross-sectional areas are stored, which can be used for comparison with determined depth profiles, cross-sectional areas or static evaluations to verify the security document under investigation. It is likewise possible that the evaluation device has an interface 27 includes, can be retrieved via the default values from a database. It is equally possible to provide measurement results and / or a verification decision via the interface 27 output, which may be formed as a wired interface or as a radio interface, etc.

In 2 is a schematic section of a security document 12 shown, which consists of three different substrate layers 31 . 32 . 33 is formed. In the document, information is coded by ink jet printing. On the middle substrate layer 32 are three print pixels 34 . 35 . 36 printed. Here, part of the printing ink is in the middle substrate layer 32 and the underlying substrate layer 33 diffused. Overall, the substrate layers 31 to 33 for example, in a lamination process to a document body 40 together. In a study of a depth profile, the significant extension is not only in the lateral direction 37 but also in the vertical direction 38 , which are perpendicular to the substrate layer surface 39 the substrate layer 32 oriented, perceptible. The in the document body 40 Stored information can thus be distinguished from an information that is applied with another printing method, in which no or not so pronounced diffusion of the colorant into the substrate layers 32 . 33 takes place.

In 3a and 3b are further excerpts of a document body 40 shown schematically. In 3a is shown in the document body 40 first a conical recess 41 is introduced. The individual substrate layers 31 to 33 are preferably all transparent and provided here only for reasons of simplified representation by means of different hatching. However, the substrate layers may have different refractive indices. In 3b the finished document body is shown, in which the conical recess 41 with a preferably also transparent filler 42 is filled. A refractive index of the filler 42 preferably differs slightly from the refractive indices of the materials making up the substrate layers 31 to 33 are made. When creating a depth profile of the document body can be the filled recess 41 based on the changes in the originally flat boundary layers 44 and 45 prove.

In 4 is a cross-sectional area formed on the basis of several juxtaposed depth profiles 25 shown schematically. The different positions are plotted along the X axis and the different depths along the Y axis. The assigned intensity values are graduated in color or gray scale. The intensity values assigned to a position for the different depth values represent a depth profile. In the example shown, only intensity values that are characteristic for transitions from one material layer to the other material layer are shown for the sake of simplicity. The remaining depth values at which no boundary surface is detected, here is assigned an intensity value of zero. The boundary layers 44 and 45 as well as the outer surface 15 are in the illustrated from the depth profiles derived cross-sectional area 25 clearly visible. In addition, intensity values corresponding to characteristic substrate transitions can be seen at those edges which are the introduced and filled recess 41 limit.

It can be clearly seen that such a cross-sectional surface representation differs significantly from a cross-sectional representation, as in 5 in which a representation for a similar security document is shown by way of example, which does not include the padded conical recess. The surface 15 as well as the two layer boundaries 44 . 45 , which are not modified, are clearly visible.

Alternatively, it is possible to carry out statistical evaluations. If, for example, one plots the frequency as a function of the assigned depth value for a selected intensity value or an intensity value range, then one obtains for the document without the filled recess, for example, a view as shown in FIG 6 is shown. There are three sharply defined local elevations 53 - 55 , which all have about the same frequency and the surface 15 as well as the layer transitions 44 . 45 can be assigned.

In 7 the same statistical evaluation is shown for the security document with the filled cone-shaped recess. Again, the three are the surface 15 and the layer boundaries 44 . 45 attributable increases 53 - 55 however, it is also over a wide depth range 56 also a finite number 57 of intensity values which are due to the cone walls running obliquely through the document 43 caused (see. 3b ).

In 8th and 9 Statistical evaluations are shown in which the intensity values occurring in a given depth range are plotted as a function of their frequency. While in a verification of a non-manipulated layer boundary ( 8th ) almost exclusively the intensity values characterizing a stratum transition 61 are observed in the distribution after 9 that corresponds to a document having a manipulated layer boundary, in the depth region around the layer boundary, not only the intensity values characterizing a layer transition 61 , but also a variety of other intensity values present with the reflection property of the bulk material 62 or with other transitions 63 correspond, which occur between the substrate and an adhesive used, for example, or between the adhesive and the second substrate layer. It can be seen that a manipulation can also be clearly seen from the comparison of these two spectra.

Again, another evaluation may provide that, for example, the depth values of a depth value range 71 (Comp. 4 ) to which intensity values or intensity value changes above a threshold value or within a value range are assigned are to be plotted against the corresponding position. In 10 a resulting graphical representation is shown. For evaluation, the depth values are parameterized 72 the position f (x, t1, t2, a, b, c) adapted. The function 72 is shown as a solid line. Is the function 72 optimally adapted, the parameters t1, t2, a, b, c characterize the tip of the recess 41 , b indicates the center position. Δt = t2 - t1 indicates the depth of the tip and the difference a - c a width of the tip at the boundary layer at the depth t1. A comparison of the parameter values with specifications thus makes verification possible.

It is understood that only exemplary evaluations are described here. It goes without saying that the individual evaluations can be carried out combined and complex evaluations can be carried out in order to identify different security features in the examined documents or to prove their absence. For example, a surface relief can be scanned and compared with a preset. The individual features described may be used in any combination to carry out the invention.

LIST OF REFERENCE NUMBERS

1

verification device

2

White Light Interferometer

3

light source

4

light

4m

Share of light sent to the arm

4mR

Proportion of light reflected back from the measuring arm

4r

Share of light sent to the reference arm

4RR

Proportion of light reflected back from the reference arm

5

optical element

6

beamsplitter

7

reference arm

8th

The End

9

mirror

10

actuator

l _r

reference arm

l _m

Messarmlänge

11

measuring arm

12

document recording

13

The security document

14

detector

15

surface

P1, P2, P3

positions

16

volume

17

Control and data acquisition device

19-1-19-3

investigation direction

20

route

21

evaluation

23

display device

24

display area

25

Cross sectional area

26

storage device

27

interface

31, 32, 33

substrate layers

34, 35, 36

pressure pixels

37

lateral direction

38

vertical direction

39

Substrate layer surface

40

document body

41

recess

42

filling material

43

cone walls

44, 45

boundary layers

53-55

local elevations

56

Deep Range

57

number

61

a layer transition characterizing intensity values

62

Volume characteristics characterizing intensity values

63

other layer transitions characterizing intensity values

71

Deep Range

72

function

t1, t2

Parameter values for depths

a, b, c

Parameter values for positions

Claims (10)

Method for verifying a security document ( 13 ) comprising the steps of: orienting the security document ( 13 ) relative to a white light interferometer ( 2 ), Performing a white light interferometric examination on at least one location (P1-P3) of a surface ( 15 ) of a security document ( 13 ), wherein a depth profile along an examination direction ( 19-1 to 19-3 ), deriving a feature from the depth profile and comparing the at least one derived feature with one or more constraints to derive a verification decision. Method according to claim 1, characterized in that the security document ( 13 ) is oriented so that the examination direction ( 19-1 to 19-3 ) perpendicular to a surface ( 15 ) of the security document ( 13 ) is oriented. Method according to claim 1 or 2, characterized in that for a plurality of locations (P1 to P3) that travel together along a route ( 20 ) on the surface ( 15 ) of the security document ( 13 ) or for a plurality of locations (P1 to P3) located in a surface area of the surface ( 15 ) of the security document ( 13 ), which comprises the at least one location (P1), depth profiles are recorded simultaneously with the depth profile for the at least one location (P1). Method according to one of the preceding claims, characterized in that on a display device ( 23 ) at least one cross-sectional area determined from the acquired depth profiles ( 25 ) of the security document ( 13 ) displayed by the examination direction ( 19-1 to 19-3 ) and the route ( 20 ) or a contour lying in the surface area is clamped. Method according to one of the preceding claims, characterized in that the intensity values and / or intensity value changes of a plurality of depth profiles corresponding to individual depth values or depth ranges are statistically evaluated with respect to their frequency in order to determine a deviation from an expected statistical distribution as an indication of a manipulation or forgery. Method according to one of the preceding claims, characterized in that depth values at which intensity values or intensity value changes, which in each case via a comparison of an intensity value with the intensity value of an adjacent spatial position in the security document ( 13 ) or with the intensity values of adjacent spatial positions in the security document ( 13 ), above a threshold, or within a range of values bounded by an upper threshold and a lower threshold, are evaluated in frequency to determine deviations or matches of one or more expected statistical distributions, and to derive therefrom the verification decision. Method according to one of the preceding claims, characterized in that in at least one cutout or depth range of the at least one cross-sectional area ( 25 ) the depth values to which intensity values of a value range are assigned, or the depth values to which intensity value changes of a value range are assigned, with respect to their assigned positions (P1 to P3) along the at least one distance or curve, are approximated by a predetermined parameterized function of the position and in the approximation derived parameters (t1, t2, a, b, c) the verification decision is made. Verification device ( 1 ) comprising a document recording ( 12 ) and a white light interferometer ( 2 ), which is designed for at least one position (P1) on a surface ( 15 ) one on or in the document recording ( 12 ) ( 13 ) a depth profile along a transverse to the surface ( 15 ) oriented examination direction ( 19-1 ), and an evaluation device ( 21 ), which evaluates the at least one depth profile. Verification device ( 1 ) according to claim 8, characterized in that the white light interferometer ( 2 ) is designed as an optical coherence tomograph. Verification device ( 1 ) according to one of claims 8 or 9, characterized in that the white light interferometer ( 1 ) a light source ( 3 ), a beam splitter ( 6 ), a detector ( 14 ), one on a controllable linear actuator ( 10 ) mounted reflector ( 9 ) and a control and data acquisition device ( 17 ), wherein the light source ( 3 ) broadband, spatial coherence ( 4 ) and so with respect to the beam splitter ( 6 ) is arranged, that the beam splitter ( 6 ) a portion of the light ( 4m ) in a measuring arm ( 11 ), in which the document recording ( 12 ), and a portion of the light ( 4r ) a reference arm ( 7 ), in which the reflector ( 9 ) is arranged so that this the light ( 4RR ) on the beam splitter ( 7 ) and reflected there with light ( 4mR superimposed on one in or on the document recording ( 12 ) arranged security document ( 13 ) to the beam splitter ( 6 ) is reflected back, whereby the detector ( 14 ) is arranged so that this in the superposition of the reflected light ( 4RR ) of the reference arm ( 7 ) with the reflected light ( 4mR ) of the measuring arm ( 11 ) can detect the resulting interference signal, wherein the control and detection device ( 17 ) with the linear actuator ( 10 ) during the detection of the interference signal, a reference arm length (l _r ) via a linear displacement of the reflector ( 9 ), the reference arm lengths (l _r ) corresponding to measuring arm lengths (l _m ), the distances from the beam splitter ( 6 ) along the examination direction ( 19-1 to 19-3 ), at least to the surface ( 15 ) of the security document ( 13 ) on or in the document recording ( 12 ) and into the interior of the security document ( 13 ) pass.

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