Valuable document having a security element with an interference layer stack and testing method

Abstract

The invention relates to a security document (10) comprising a security document substrate (12) and a security element (14) applied to the substrate. The security element (14) contains an interference layer stack (20) that gives the security element (14) an optically variable appearance when viewed visually in reflection. The interference layer stack (20) provides a characteristic IR signature as a first authentication feature, and the security document substrate (12) contains a background layer (30) on its surface, impregnated with an IR absorber (32), as a second authentication feature. This background layer is located at least partially beneath the security element (14). The first and second authentication features together form a machine-verifiable authentication mark in the infrared spectrum, the absence or incompleteness of which indicates manipulation of the security document (10).

Description

[0001] The invention relates to a value document comprising a value document substrate and a security element applied thereto with an interference layer stack that imparts an optically variable appearance to the security element upon visual reflection. The invention also includes a method for verifying such a value document.

[0002] Data storage media, such as valuables or identification documents, but also other valuable items, such as branded goods, are often provided with security elements for security purposes. These elements allow the authenticity of the data storage media to be verified and at the same time serve as protection against unauthorized reproduction.

[0003] For this purpose, optically variable security elements are often used, whose special visual effect, such as a color-shift effect, can be identified by the naked eye without any additional aids. However, such Level 1 features are often subject to so-called "harvesting" attacks, in which a counterfeiter removes ("harvests") the security element from a genuine document and attaches it to a fake, such as a photocopy, thereby visually enhancing it.

[0004] There is therefore a need for technical solutions that can reliably detect such manipulated banknotes and other valuable documents during machine processing / sorting.

[0005] Foil-based security elements often do not carry machine-readable features, so that the replacement of such a foil-based security element with a counterfeit cannot be easily detected by machine.

[0006] If, to remedy this, a foil-based security element is printed with an IR absorber, for example in non-metallized areas, the absence of the genuine security element on a value document can be detected with IR remission sensors, but a counterfeit with the transferred (genuine) foil is assessed as genuine.

[0007] In WO 2023 / 285000 A1, it was therefore proposed to provide both the substrate of a banknote and an applied security element with security components that, in combination, provide a characteristic signal. The absence of the combination signal then represents a strong indication of tampering. In particular, two different IR absorbers, each absorbing in spectrally separate ranges, are used to mark the substrate and the foil, respectively. This requires, on the one hand, the integration of an IR absorber into transparent, non-metallized areas of the foil element, which requires larger demetallized areas and thus represents a significant limitation of the foil design.Furthermore, a combination of two spectrally separated IR absorbers represents a significant hurdle in practice, since most IR absorbers absorb broadband and therefore spectrally overlap in the limited spectral range of the commonly used, inexpensive IR sensors (750 nm to 1050 nm).

[0008] Based on this, the invention is based on the object of providing a generic security document that avoids the disadvantages of the prior art and, in particular, in which a security document manipulated by a detachment attack can be reliably detected by machine. The invention also aims to provide a verification method for security documents secured in this way.

[0009] This object is achieved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

[0010] The invention includes a value document comprising a value document substrate and a security element applied to the substrate, wherein the security element includes an interference layer stack which gives the security element an optically variable appearance when visually observed in reflection.

[0011] The interference layer stack provides a characteristic IR signature as a first authenticity feature of the value document.

[0012] As a second authenticity feature of the value document, the value document substrate contains on its surface a background layer containing an IR absorber, which is arranged at least partially beneath the security element.

[0013] In a first application, the value document substrate itself can be made of paper, such as in the case of paper banknotes or visas. In another application, such as in the case of polymer banknotes, ID cards, or driver's licenses, the value document substrate can be made of a polymer, e.g., polycarbonate or polypropylene, or of a polymer composite. In other applications, paper-polymer hybrid composite materials, such as laminated paper layers, can also be used as the value document substrate.

[0014] The first and second authenticity features together form an infrared-machine-verifiable authenticity mark, the absence or incompleteness of which indicates tampering with the valuable document. In particular, the absence of the first or second authenticity feature can be used to infer tampering with the valuable document. As explained in more detail below, with the invention, both the donor document with a detached security element and the recipient document with a transferred, genuine security element can be detected as tampered with.

[0015] It is particularly advantageous that the adhesion of the background layer containing the IR absorber to the substrate is higher than the adhesion to the security element, so that the second authenticity feature remains essentially completely on the value document substrate when the security element is removed.

[0016] "Substantially complete" means that more than 90%, more than 94% and in particular more than 98% of the IR absorber remains on the value document substrate.

[0017] The background layer is preferably formed by a primer layer or an imprint. In the case of a paper security document substrate, the background layer is preferably formed by a paper primer. A paper primer or a suitable imprint can form a particularly close bond with the security document substrate, so that when the security element is removed, an adhesive failure occurs at the interface with the underlying background layer, and the security element is removed without the background layer.

[0018] In an advantageous embodiment, the background layer is arranged partly below and partly next to the security element. The presence of the IR absorber can then also be detected in areas adjacent to the security element.

[0019] In another, equally advantageous embodiment, the background layer is arranged entirely beneath the security element. The latter has the advantage that no additional space is required on the valuable document for the additional protection provided by the IR absorber, and authenticity verification can be performed independently of the valuable document's print design.

[0020] In an advantageous embodiment, the interference layer stack is formed by a color-shifting thin-film element. The thin-film element can, for example, have a three-layer structure consisting of an absorber layer, a dielectric spacer layer, and a reflector layer, or a five-layer structure consisting of a first absorber layer, a first dielectric spacer layer, a second absorber layer, a second dielectric spacer layer, and a reflector layer. Five-layer structures offer a particular advantage by providing additional degrees of freedom in optical design, as they allow the generation of different IR spectral profiles and thus different IR signatures with a similar or identical visual appearance.Therefore, an observed visual effect, for example a certain color change when tilting the security element, cannot easily be used to determine the IR signature of the interference layer stack, making it very difficult to recreate the effect.

[0021] The reflector layer is preferably opaque and can be made of aluminum, for example. The absorber layer or layers are advantageously formed by semitransparent chromium layers. The dielectric spacer layers can be made of SiO2, in particular.

[0022] The security element advantageously contains a metal layer, which is preferably formed by the reflector layer of the interference layer stack. However, it is also possible for the metal layer to be an additional layer arranged above or below the interference layer stack.

[0023] The metal layer of the security element is advantageously structured at least in partial areas. In particular, the metal layer of the security element can have a structured partial area with narrow metallic bars, narrow metallic lines, and / or metallic patterns and / or characters of thin line width, wherein the area coverage of the metal layer in said structured partial area is preferably below 20%, in particular below 15% or even below 10%. Surprisingly, it has been found that the IR detection of an underlying background layer is not significantly impaired by such narrow metallic structures. The narrow metallic structures therefore allow greater design freedom for the designer without compromising the technical function of the security element during authentication.The geometric dimension of the structured sub-area is preferably selected such that it has an area of ​​at least 8 mm², preferably at least 20 mm². In this case, the presence of the IR absorber in the substrate layer can be reliably detected even with inexpensive IR sensors, which may only have a limited spatial resolution in the millimeter range.

[0024] The IR absorber of the substrate layer is advantageously essentially transparent or white in the visible spectral range and thus visually unobtrusive. While the IR absorber can generally absorb both spectrally broadly and spectrally narrowband, IR absorbers that absorb broadband in the near-infrared (NIR) range from 700 nm to 1500 nm, especially in the range from 750 nm to 1100 nm, are currently particularly preferred.

[0025] Suitable IR absorbers can be found, for example, in WO 2007 / 060133 A1, the disclosure of which is incorporated into the present application in this respect. Examples of suitable IR absorbers include iron(II) or copper(II) compounds with an Fe2+ ion or a Cu2+ ion in a suitable chemical environment, where a suitable chemical environment is, for example, a phosphate ion or a polyphosphate ion or, more generally, a group containing phosphorus and oxygen. Such IR absorbers absorb broadly in the NIR range from 700 nm to 1100 nm, but are essentially transparent or white in the visible spectral range, exhibiting at most a slightly yellowish, greenish, or bluish tint. The presence of the IR absorber in the background layer is therefore barely detectable visually.

[0026] Also suitable as IR absorbers are the IR substances sold under the name LUMOGEN-S by BASF Corporation, 100 Park Ave., Florham Park, NJ 07932, the IR-absorbing materials disclosed in GB 2 168 372, which are invisible or transparent in the visible range of the electromagnetic spectrum, and the IR markers disclosed in US Pat. No. 6,926,764. These IR markers are substituted naphthalocyanines, phthalocyanines, metal-containing phthalocyanines, or polysubstituted phthalocyanines. Thiophenol-substituted copper phthalocyanines, especially para-toluenethiol-persubstituted copper phthalocyanines, are preferred.

[0027] In an advantageous development of the invention, the security element contains a relief structure arranged beneath the interference layer stack. The relief structure can be formed, in particular, by a micromirror arrangement with directionally reflecting micromirrors, in particular a micromirror arrangement with non-diffractive mirrors. However, the relief structure can also be formed by a diffractive diffraction structure, in particular a hologram structure, nanostructure, or diffractive blazed grating. Such relief structures allow the security element to exhibit a motion effect or a three-dimensional appearance in addition to the color-shift effect of the interference layer stack, thus visually enhancing its forgery security and increasing its security against counterfeiting.

[0028] In advantageous embodiments, the security element contains a film layer, in particular a film layer that is transparent in the visible spectral range and advantageously also in the near infrared. The security element advantageously covers a continuous opening in the value document substrate with the film layer. In other embodiments, the security element can be constructed during production on a transfer film, which is removed again after the security element has been transferred to the value document.

[0029] The invention also includes a method for checking a value document of the type described, in which the value document is exposed to infrared radiation at least in the area of ​​the security element at several locations and the remitted IR radiation is detected, the presence of the characteristic IR signature of the first authenticity feature and the presence of the IR response of the IR absorber of the second authenticity feature are each determined in a spatially resolved manner on the basis of the detected remitted IR radiation, and the authenticity of the value document is assessed on the basis of the presence and the determined distribution of the first and second authenticity features.

[0030] In particular, it can be checked whether both the first and second authenticity features are present. If one of the two authenticity features is missing, it can be concluded that the value document has been tampered with. Even if both authenticity features are present, a distribution of the authenticity features that deviates from the expected spatial distribution can be used to conclude that the document has been tampered with.

[0031] Further embodiments and advantages of the invention are explained below with reference to the figures, in which a true-to-scale and true-to-proportion reproduction has been omitted in order to increase clarity.

[0032] They show: Fig. 1 schematically shows a banknote according to an embodiment of the invention in plan view, Fig. 2 a cross section of the banknote of the Fig. 1 along the line II-II, Fig. 3in (a) a section of the unmanipulated banknote of the Fig. 1 together with four measuring tracks for the authenticity test, and in (b) schematically the measurement result in the four measuring tracks of (a), Fig. 4 in (a) a section of a manipulated banknote in which a detached foil strip was transferred to an unauthorized substrate, and in (b) schematically the measurement result in the four measuring tracks of (a), Fig. 5 in (a) a section of another manipulated banknote in which the paper substrate of a donor banknote was provided with a counterfeit foil strip after the original foil strip had been detached, and in (b) schematically the measurement result in the four measuring tracks of (a), Fig. 6 schematically a banknote according to another embodiment of the invention in cross section, and Fig. 7 in (a) a plan view of a banknote according to the embodiment of the Fig. 6 and in (b) the spatially resolved IR signal detectable by an IR sensor.

[0033] The invention will now be explained using banknotes as an example. Fig. 1 shows a schematic top view of a banknote 10, on whose paper substrate 12 a security element in the form of a partially metallized foil strip 14 is applied. Figur 2 shows a cross-section of banknote 10 in the area of ​​the security element along line II-II of the Fig. 1 .

[0034] The film strip 14 contains a film carrier 16, for example, a thin, e.g., 4 µm - 40 µm thick PET film that is transparent in the visible and near-infrared spectral ranges, which is provided with a color-shifting interference layer stack 20 in a partial region 18. In the illustrated embodiment, the interference layer stack 20 is formed by a three-layer thin-film interference layer system with a reflector layer 22, for example, an opaque aluminum layer, a dielectric spacer layer 24, for example, a 420 nm thick SiO 2 layer, and an absorber layer, for example, an 8 nm thick chromium layer.

[0035] When viewed in reflection, the interference layer stack 20 not only exhibits interference maxima in the visible spectrum from 380 nm to 780 nm, but also exhibits interference maxima in the near-infrared range between 780 nm and 3000 nm. These NIR interference maxima are intrinsically linked to the layer structure responsible for the visual color-shift effect of the interference layer stack 20, in particular the specific thickness of the dielectric spacer layer 24, and are equally present for all security elements with this layer structure, so that the interference layer stack 20 provides a characteristic IR signature as a first authenticity feature.

[0036] How best in Fig. 2 As can be seen, a substrate layer 30 is applied to the paper substrate 12 beneath and partially also adjacent to the film strip 14. This substrate layer is mixed with an IR absorber 32 and can be present, in particular, in the form of a paper primer or a print. The substrate layer 30 exhibits high adhesion to the paper substrate 12; in particular, the adhesion of the substrate layer 30 to the paper substrate 12 is higher than to the film strip 14.

[0037] The IR absorber 32 is ideally transparent in the visible spectral range and exhibits at most a slight tint. The presence of the background layer 30 is therefore visually unobtrusive, so that the position and extent of the background layer 30 can be determined in Fig. 1 are only indicated by dashed lines.

[0038] The background layer 30, which is offset with the IR absorber 32, forms a second authenticity feature of the banknote 10, and the first and second authenticity features together form an infrared-machine-verifiable authenticity mark of the value document. During an authenticity check, the complete presence and correct position of both authenticity features can serve as proof of the authenticity of the banknote 10, while the absence of one of the two authenticity features or a deviating position or extent of one of the authenticity features indicates tampering with the banknote 10.

[0039] For illustration, Fig. 3 In (a), a section of the unmanipulated banknote 10 with four measuring tracks 40, 42, 44, 46, in which the IR remission of the banknote 10 is measured spectrally by an IR sensor during the authentication. Measuring the IR remission at several different wavelengths allows the characteristic IR signature of the interference layer stack 20 to be distinguished from the IR signature of other interference layer stacks with different layer structures, and in particular from the IR remission of IR absorber materials.

[0040] Figur 3(b) shows schematically the measurement result on banknote 10 in the four measuring tracks of the Fig. 3(a) . The measuring tracks 40 and 46 lie outside the partial area 18 provided with the interference layer stack in an infrared-transparent area of ​​the carrier film 16. In these measuring tracks, the sensor therefore detects the IR remission 50 of the IR absorber 32 of the background layer 30 both below and next to the film strip 14.

[0041] The measurement tracks 42, 44 also cover the partial area 18 with the interference layer stack 20. To the right and left of the interference layer stack 20, the sensor measures the IR remission 50 of the IR absorber 32 of the background layer 30. In the partial area 18, however, the sensor only detects the characteristic IR signature 52 of the interference layer stack 20, while the IR absorber 32 located beneath the foil strip 14 is shielded by the metallic reflection layer 22 of the interference layer stack 20 and makes no contribution to the IR signal.

[0042] The positions and sizes of the areas with recorded IR remission 50 or IR signature 52 in the four measuring tracks 40-46 are then compared with expected positions and sizes and, if they match, the banknote is assessed as genuine.

[0043] During a harvesting attack, in which the interference layer stack 20 with its visual color-shift effect is removed from the banknote 10, the IR signature generated by the layer sequence of the interference layer stack 20, and thus the first authenticity feature, is inevitably also removed from the banknote 10. On the other hand, the background layer 30 with the IR absorber 32 remains essentially completely on the paper substrate 12 of the donor banknote due to its high adhesion to the paper substrate 12, even when the foil strip 14 is removed.

[0044] Figur 4 (a) shows a section of a manipulated banknote 10-V1, in which the foil strip 14 detached from the authentic banknote 10 was transferred to an unauthorized substrate 12-V, for example, a photocopy. The background layer remaining on the original paper substrate 12 was not transferred during the removal attack and is therefore not present on the substrate 12-V.

[0045] Figur 4(b) shows schematically the measurement result on the manipulated banknote 10-V1 during the authenticity test in the four measuring tracks of the Fig. 3 . In the measuring tracks 40, 46, which lie outside the partial area 18, no IR signal is detected due to the absence of the background layer 30 and the IR absorber 32.

[0046] In the measuring tracks 42, 44, which intersect the partial area 18 with the interference layer stack 20, the characteristic IR signature 52 of the transferred interference layer stack 20 is recorded; however, the IR remissions of the IR absorber to the right and left of the interference stack 20 are missing in these measuring tracks.

[0047] When comparing the positions and sizes of the areas with recorded IR remission 50 or IR signature 52 in the four measuring tracks 40-46, it can be clearly concluded that the banknote 10-V1 has been tampered with due to the absence of IR remission 50 in all four measuring tracks.

[0048] Figur 5 shows in (a) a section of another manipulated banknote 10-V2, in which the paper substrate 12 of the donor banknote was provided with a counterfeit foil strip 14-V in the area of ​​the background layer 30 after the original foil strip 14 had been removed.

[0049] Often, simple photocopies or printed strips without a color-shift effect are used for such counterfeits, which consequently do not produce a specific IR signature 54. Even in more complex counterfeits with a color-shift effect, the counterfeiter does not know the exact layer thickness of the dielectric spacer layer 24, so that the interference layer stack of the counterfeit foil strip 14-V in the partial area 18, even with a comparable visual appearance, will produce a different IR signature 54 than the original foil strip 14, as indicated in the figure by a different hatching. In addition, the counterfeiter may not know the exact position of the foil strip on the banknote and / or the significance of the precise alignment of the interference layer element relative to the background layer 30, so that the position of the partial area 18 may be different from the original banknote 10, as shown in Fig. 5(a) also shown.

[0050] Figur 5(b) shows schematically the measurement result on the manipulated banknote 10-V2 during the authenticity test in the four measuring tracks of the Fig. 3 In the measuring tracks 40, 46, which lie outside the partial area 18, the sensor detects the IR remission 50 of the IR absorber 32 of the background layer 30 both below and next to the foil strip 14-V. Since the banknote 10-V2 contains the original paper substrate 12, the measured IR remission 50 corresponds to the expected remission.

[0051] However, in the measurement tracks 42, 44 that intersect the partial area 18 with the interference layer stack 20, the IR signature 54 of the counterfeit foil strip 14-V is detected instead of the expected IR signature 52. Furthermore, the determined position of the partial area 18, particularly relative to the position of the background layer 30, deviates from the expected position.

[0052] By comparing the positions and sizes of the areas with recorded IR remission 50 or IR signature 54 with the expected positions and sizes and by comparing the IR signature 54 with the expected, correct IR signature 52, it can also be clearly concluded that the banknote 10-V2 has been manipulated.

[0053] Further advantageous embodiments and modifications will now be described with reference to Fig. 6 und 7 explained, it being understood that not all modifications shown in these figures need to be made simultaneously.

[0054] The combination of an IR-absorbing background layer beneath an optically variable security element, combined with narrow demetallized gaps in the metal-containing interference layer stack and / or with predominantly transparent areas with fine metallized bars, lines, characters, or patterns, has proven particularly attractive. Surprisingly, such fine metal structures barely impair the detection of the underlying IR absorber, while, on the other hand, narrow demetallized gaps barely affect the detection of the IR signature of the interference layer stack.

[0055] For illustration, Fig. 6 schematically a banknote 10 with a background layer 30 provided with an IR absorber 32 and a foil strip 80 arranged on the background layer 30 in cross section, and Fig. 7 shows in (a) a section of a banknote 10 with such a foil strip 80 in plan view and in (b) the spatially resolved, associated IR signal measured by an IR sensor.

[0056] In the examples of the Fig. 6 und 7 the background layer 30 is located exclusively beneath, but not adjacent to, the foil strip 80. This has the advantage that no additional space is required on the banknote 10 for the combined protection provided by the first and second authenticity features, and that the authenticity of the banknote can be verified locally in the area of ​​the foil strip 80, regardless of the banknote's print design.

[0057] Another special feature is the foil strip 80 in the design of the Fig. 6 provided with a more complex interference layer stack 60, namely a 5-layer thin-film interference layer system comprising an opaque aluminum layer as reflector layer 62, a 280 nm thick dielectric SiO 2 layer as second dielectric spacer layer 64, a 3 nm thick chromium layer as second absorber layer 66, a 140 nm thick dielectric SiO 2 layer as first dielectric spacer layer 68, and a 5 nm thick chromium layer as first absorber layer 70. Such 5-layer systems enable additional degrees of freedom in optical design, as they permit the generation of different IR spectral profiles and thus different IR signatures with similar or identical visual color-shift effects. A potential counterfeiter cannot therefore deduce the IR signature of the interference layer stack 60 from the visual color-shift effect.

[0058] As a further special feature, the aluminum layer 62 of the interference layer stack 60 is present in a first partial region 82 of the film strip 80 only in the form of narrow metal webs 84, so that the partial region 82 is largely transparent. In the partial region 86, however, the film strip is essentially opaque, with the aluminum layer 62 covering the entire surface except for narrow recesses 88. The area coverage of the metallization in the partial region 86 is above 80%, preferably above 90%.

[0059] Fig. 7 (a) shows an exemplary design in which the narrow metal bars 84 in sub-area 82 form a regular square grid and, at two locations, the value number "10" executed with a narrow line width. In sub-area 86, the recesses 88 form a geometric shape or pattern. The area coverage of the metallization is below 20% in sub-area 82, but above 80% in sub-area 86.

[0060] How Fig. 7(b) As illustrated, the IR detection is not impaired by the metallic webs 84 or the narrow recesses 88. Rather, the sensor continuously detects the IR remission 50 of the IR absorber 32 in the partial area 82 and the IR signature 56 of the interference layer stack 60 in the partial area 86.

Claims

1. A value document with a value document substrate and a security element applied to the substrate, which contains an interference layer stack which gives the security element an optically variable appearance when viewed visually in reflection, wherein - the interference layer stack provides a characteristic IR signature as a first authenticity feature, - the value document substrate contains, as a second authenticity feature, on its surface a background layer mixed with an IR absorber, which is arranged at least partially beneath the security element, - wherein the first and second authenticity features together form an authenticity mark which can be machine-tested in the infrared, the absence or incompleteness of which indicates tampering with the value document.

2. Value document according to claim 1, characterized in thatthe adhesion of the background layer containing the IR absorber to the substrate is higher than the adhesion to the security element, so that the second authenticity feature remains essentially completely on the value document substrate when the security element is removed, 3. A value document according to claim 1 or 2, characterized in that the substrate layer is formed by a print or a primer layer, in particular a paper primer.

4. Value document according to at least one of claims 1 to 3, characterized in that the substrate layer is located completely beneath the security element.

5. A value document according to at least one of claims 1 to 4, characterized in thatthe interference layer stack comprises a color-shifting thin-film element, in particular with a three-layer structure comprising an absorber layer, a dielectric spacer layer and a reflector layer, or with a five-layer structure comprising a first absorber layer, a first dielectric spacer layer, a second absorber layer, a second dielectric spacer layer and a reflector layer.

6. A value document according to at least one of claims 1 to 5, characterized in that the security element contains a metal layer, which is preferably formed by the reflector layer of the interference layer stack.

7. A value document according to at least one of claims 1 to 6, characterized in that the metal layer of the security element is structured at least in some areas.

8. Value document according to claim 7, characterized in thatthe metal layer of the security element has a structured partial area with narrow metallic bars, narrow metallic lines and / or metallic patterns of low line width, wherein preferably the area of the structured partial area is at least 8 mm 2 , particularly preferably at least 20 mm 2 and the area coverage of the metal layer in the said structured partial area is preferably below 20%.

9. A value document according to at least one of claims 1 to 8, characterized by the IR absorber is essentially white or transparent in the visible spectral range.

10. A value document according to at least one of claims 1 to 9, characterized in that The IR absorber absorbs broadband radiation in the near-infrared range from 700 nm to 1100 nm.

11. A value document according to at least one of claims 1 to 10, characterized in thatthe security element contains a relief structure arranged below the interference layer stack, wherein the relief structure is preferably formed by a micromirror arrangement with directionally reflecting micromirrors, in particular with non-diffractive mirrors, or by a diffractive diffraction structure, in particular a hologram structure, nanostructure or diffractive, blazed grating.

12. A value document according to at least one of claims 1 to 11, characterized in that the security element contains a film layer, in particular a film layer that is transparent in the visible spectral range and advantageously additionally in the near infrared.

13. Value document according to claim 12, characterized in that the security element with the foil layer covers a continuous opening in the value document substrate.

14. Method for checking a value document according to one of claims 1 to 13, in which - the value document is exposed to infrared radiation at least in the area of the security element at several locations and the remitted IR radiation is detected, - the presence of the characteristic IR signature of the first authenticity feature and the presence of the IR response of the IR absorber of the second authenticity feature are each determined in a spatially resolved manner on the basis of the detected remitted IR radiation, and - the authenticity of the value document is assessed on the basis of the presence and the determined distribution of the first and second authenticity features.

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