Personalizable security document

Abstract

A personalizable security document (10) includes a hidden pattern (4b) that is formed in an image-forming region (2, 3) configured to have a personalized image laser-engraved in the same. The hidden pattern (4b) is formed by a polarization-changing material layer, which changes the polarization of light passing through the same. The pattern (4b) is not visible when the security document (10) is viewed under white light in reflection. The pattern (4b) becomes visible when the security document (10) is viewed under white light through a polarization filter (20).

Description

Technical Field

[0001] The present disclosure generally relates to security features for security documents, in particular, personalizable security documents such as identification documents, driver's licenses and the like.Background

[0002] Generally, in the market of physical identification documents, a variety of different security features is used. In some applications, a laser engraved image is considered vital, as the image features are obtained inside a polycarbonate substrate rather than on the surface of the substrate. A laser engraved feature in a polycarbonate substrate may include a black and white (in particular, grayscale) image, a color image, or other special features.

[0003] Examples for other kinds of security features include the use of a combination of laser and ink to secure the document. Other ways to secure the document are the use of holograms embedded inside the security document in order to secure a main portrait or a secondary portrait of a holder of the security document. If the portrait is tampered with, the hologram will also be altered, resulting in an additional layer of protection.

[0004] Also known is the use of fluorescent inks, which are applied to the security document during manufacturing of the same, and which can be observed under ultraviolet (UV) light, adding an extra layer of security to the security document.

[0005] The present disclosure is directed, at least in part, to further increasing the security of personalizable security documents, without being limited to a particular type of security document.Summary of the Disclosure

[0006] According to one aspect of the present disclosure, a personalizable security document has a substrate having a first side and a second side opposite to the first side in a thickness direction of the substrate, an image-forming region provided in the substrate and configured to have a personalized image laser-engraved in the same from the first side, and a security feature provided in the substrate. The security feature includes a polarization-changing material layer configured to change a polarization of light passing through the same. The polarization-changing material layer forms a pattern overlapping at least in part the image-forming region. The pattern is not visible when the substrate is viewed from the first side under white light in reflection, and becomes visible when the substrate is viewed from the first side under white light through a polarization filter.

[0007] In another aspect of the present disclosure, a method of personalizing a security document includes the steps of providing a personalizable security document in accordance with the above aspect, and laser engraving a personalized image in the image-forming region by varying one or more laser parameters. Preferably, a laser power during engraving is less than 30 W, more preferably less than 20 W.

[0008] In a further aspect, the present disclosure relates to a device for verifying a security feature of a personalized security document, the security features including a polarization-changing material layer configured to change a polarization of light passing through the same. The device has a light source configured to emit light in the visible range towards the security document, a camera configured to capture an image of a portion of the security document including the security feature, a polarization filter covering the light source and the camera, a display and a controller. The controller is configured to control the light source to emit light towards the security document via the polarization filter, control the camera to capture an image of the security document while emitting the light towards the security document, analyze the captured image to determine whether a predetermined pattern included in the security feature is present or not, and display at least one of the observed pattern and an indicator indicating a result of the determination on the display.

[0009] Other features and aspects of the present disclosure will be apparent from the following description and the accompanying drawings.Brief Description of the Drawings

[0010] Fig. 1 shows an exemplary plan view of a personalizable security document in accordance with the present disclosure; Fig. 2 shows another plan view of the exemplary personalizable security document according to the present disclosure; Fig. 3 shows a schematic cross-sectional view of the personalizable security document in accordance with the present disclosure; Fig. 4 shows a plan view of a personalized security document in accordance with the present disclosure; Fig. 5 shows another plan view of a personalized security document in accordance with the present disclosure; Fig. 6 shows a plan view of another example for a personalizable security document in accordance with the present disclosure; Fig. 7 shows a plan view of yet another example for a personalizable security document in accordance with the present disclosure; and Fig. 8 shows a schematic overview of an exemplary device for verifying a security feature in accordance with the present disclosure. Detailed Description

[0011] The following is a detailed description of exemplary embodiments of the present disclosure. The exemplary embodiments described herein are intended to teach the principles of the present disclosure, enabling those of ordinary skill in the art to implement and use the present disclosure in many different environments and for many different applications. Therefore, the exemplary embodiments are not intended to be, and should not be considered as, a limiting description of the scope of protection. Rather, the scope of protection shall be defined by the appended claims.

[0012] Hidden text is common in the market for security documents. In particular, fluorescent inks and the like can be printed over security document layers to convey hidden text or information, which can be revealed under special light such as ultraviolet (UV) and infrared (IR) light. The present disclosure combines polarization-sensitive inks, which reveal themselves under polarized light, with other security features such as a primary portrait or a secondary portrait formed by laser engraving.

[0013] A device such as a mobile phone having an appropriate configuration can be used to authenticate the security document, by verifying whether the hidden feature is present or not. For example, a mobile phone can be provided with an appropriate polarizer to emit polarized light towards the security document, and a camera of the mobile phone can be used to capture an image of the security document. The processor of the mobile phone can analyze the captured image in order to determine whether the hidden pattern is visible in the image or not.

[0014] The hidden feature can be combined with a metallic layer configured to have a personalized image laser-engraved in the same. The metallic layer generally has a relatively high reflectivity, which enhances the effect of selectively hiding and showing the hidden feature. Moreover, the metallic layer may also act as a further polarizer, resulting in that the hidden pattern may also be observed when viewed in transmission against white light. This has the advantage that the hidden feature can be made visible without the need for using a separate polarizer.

[0015] Fig. 1 shows a plan view of an exemplary security document 10 in accordance with the present disclosure. As shown in Fig. 1, security document 10 includes a substrate 1, for example, a polycarbonate or polyvinyl chloride (PVC) substrate having a substantially rectangular shape. Of course, the shape and type of security document 10 is not limited to such a configuration, and security document 10 may also be configured as a data page of a passport or the like.

[0016] In addition, as shown in Fig. 1, security document 10 also includes an image-forming region 2, 3 provided in substrate 1 and configured to have a personalized image 2a, 3a (see, for example, Fig. 4) laser-engraved in the same from a first side S1. Here, image-forming region 2, 3 may either be provided in a portion of substrate 1 configured to have a primary portrait of a holder of security document 10 laser-engraved in the same, as indicated by dashed lines in Fig. 1, or may be an image-forming region 3 that is part of a security feature including a layer of laser-engravable material 5 embedded in substrate 1 and forming image-forming region 3, as will be discussed in more detail below.

[0017] Image-forming regions 2, 3 may have any appropriate configuration, as long as it is possible to laser-engrave a personalized image in the same. For example, image-forming region 2 may simply be a portion of a substrate layer of substrate 1 on first side S1, which substrate layer may be opaque, for example, a white polycarbonate or PVC layer. Using a laser having appropriate laser power, personalized image 2a, which forms a primary or main portrait of a holder of security document 10, can be laser-engraved in a known manner.

[0018] Alternatively or in addition, image-forming region 3 may be provided as part of a security feature, and may be configured to have a secondary portrait or other personalized information laser-engraved in layer of laser-engravable material 5 in a known manner. In particular, layer of laser-engravable material 5 may exhibit a color-change upon irradiation with laser light from first side S1.

[0019] As used herein, the "color-change effect upon irradiation with laser light" means that laser light that is irradiated onto layer of laser-engravable material 5 changes at least one physical property of, for example, particles or pigments included in layer of laser-engravable material 5 in a predetermined manner, for example, depending on the intensity of the laser light, and / or other laser parameters. One particular example is the ink that is used in the Mirage security feature of HID. In this technology, each pixel in laser-engraved personalized image 3a (see Fig. 4) has a defined color value, depending, for example, on a digital grayscale value of a grayscale image to be engraved. For example, a color value of blue corresponds to white in the digital grayscale image to be engraved, and a color value of gold corresponds to black in the digital grayscale image to be engraved. This means that, for example, a minimum or zero laser power results in that laser-engravable material 5 remains of an initial blue color, whereas increasing laser power results in a color change from the initial blue color towards a golden color at maximum laser power. In between the minimum and the maximum laser power, a color-change can be observed from blue to gold. In this manner, for example, a grayscale portrait of a holder of security document 10, for example, a negative or positive image, can be formed in a surface of laser-engravable material 5.

[0020] Here, it will be appreciated that the present application is not limited to the Mirage ink described above, and can be applied to any known laser-engravable material that exhibits a color-change effect when irradiated with laser light. However, it is important to note that the color-change effect as described herein is different from a change that is obtained when a physical structure of a material layer such as a transparent PVC layer or the like is modified by being burnt using a laser having a certain power. It will be appreciated that in such a manner a grayscale image can be formed, for example, in image-forming region 2 of substrate 1, however, such a formation of a grayscale image by burning of the material of the layer is not to be understood as exhibiting a color-change effect in accordance with the present disclosure. Accordingly, as used herein, a material that exhibits a color-change effect is to be considered a material which changes its color from a first, in particular, chromatic color (for example, blue) to a second, different color (for example, golden), and a change from, for example, colorless to gray or black due to burning of material with increasing laser power is not to be considered as a color-change effect. In some embodiments, laser-engravable material 5 includes metallic pigments, for example, one or more of Al, Ag, Au, Zn, Fe and Cu pigments.

[0021] Alternatively, layer of laser-engravable material 5 may also be any other appropriately configured metallic layer exhibiting a change in reflectivity upon irradiation with laser light from first side S1. It will be appreciated that such a change in reflectivity can also be used to engrave features such as a portrait of a holder of security document 10 or other personalized information. Further, it will be appreciated that any appropriate non-metallic material, which exhibits at least one of a change in reflectivity and a color-change upon irradiation with laser light can also be used.

[0022] Returning to Fig. 1, personalizable security document 10 further includes a security feature 4 provided in substrate 1. Security feature 4 includes a polarization-changing material layer 4a (see Fig. 3) configured to change a polarization of light passing through the same. As shown in Fig. 1, polarization-changing material layer 4a forms a pattern 4b overlapping at least in part image-forming region 3. It will be appreciated that the formation of pattern 4b means that polarization-changing material layer 4a is not a continuous layer, but a layer that is structured to form pattern 4b (i.e., includes gaps or holes defining pattern 4b). This can be achieved by printing an ink including the polarization-changing material in a known manner.

[0023] As shown in Fig. 2, pattern 4b is not visible when substrate 1 is viewed from first side S1 under white light in reflection. On the other hand, pattern 4b becomes visible when substrate 1 is viewed from first side S1 under white light through a polarization filter 20, as shown in Fig. 1. In Fig. 1, pattern 4b is in the form of a hidden text, which becomes visible when polarization filter 20 is applied. It will be appreciated, however, that pattern 4b may have any appropriate configuration, for example, may be a predetermined image, which becomes visible when polarization filter 20 is applied.

[0024] As previously mentioned, in the example that is shown in Fig. 1, pattern 4b overlaps layer of laser-engravable material 5 embedded in substrate 1, which forms image-forming region 3. As also previously mentioned, layer of laser-engravable material 5 exhibits at least one of a change in reflectivity and a color-change upon irradiation with laser light from first side S1. Accordingly, by using appropriate laser light, a personalized image 3a, such as a portrait of a holder of security document 10, can be engraved in laser-engravable layer 5, with pattern 4b overlapping layer of laser-engravable material 5 and personalized image 3a. This is shown in Fig. 4. Again, as shown in Fig. 4, upon viewing personalizable security document 10 through polarization filter 20, both personalized image 3a and pattern 4b are visible.

[0025] Fig. 3 shows a schematic cross-sectional view of personalizable security document 10 in accordance with an exemplary embodiment. As shown in Fig. 3, substrate 1 includes a plurality of substrate layers 31, 32, 33, 34, 35, which may be polycarbonate or PVC layers, and polarization-changing material layer 4a and layer of laser-engravable material 5, which are formed on different ones of the plurality of substrate layers 31, 32, 33, 34, 35.

[0026] In the example that is shown in Fig. 3, polarization-changing material layer 4a is formed on a first substrate layer 32 closer to first side S1 of substrate 1 than a second substrate layer 33 on which layer of laser-engravable material 5 is formed. It will be appreciated that polarization-changing material layer 4a, more particularly, pattern 4b may be applied on substrate layer 32 prior to lamination of the plurality of substrate layers 31-35 in any appropriate manner, for example, by screen printing or offset printing using appropriate inks. In particular, polarization-changing material layer 4a may include liquid crystal particles. One exemplary ink that can be used to form polarization-changing material layer 4a, more particularly, pattern 4b is the polaCRYPT ink from the Swiss company Printcolor AG. However, the material of polarization-changing material layer 4a is not limited to this, and any appropriate ink or material that results in a change of a polarization of light passing through the same can be used. This is because the effect obtained in accordance with the present disclosure is based on the fact that, when pattern 4b is viewed via an appropriately configured polarization filter 20, only a specific polarized light (for example, linear polarized light having a specific polarization) passes through polarization filter 20 and reaches polarization-changing material layer 4a, which forms pattern 4b. Polarization-changing material layer 4a changes the specific polarization of the light passing through the same, and being reflected either by underlying portions of polarization-changing material layer 4a or underlying layers of substrate 1, for example, layer of laser-engravable material 5. This results in that the reflected light passing through pattern 4b has a different polarization than the specific polarization, and cannot pass through polarization filter 20.

[0027] Accordingly, less light that is reflected by pattern 4b reaches the observer when compared to light that is reflected by the portions of substrate 1 in which pattern 4b is not present (because said portions do not change the polarization of the reflected light). As a result, pattern 4b becomes darker and therefore becomes visible when polarization filter 20 is applied. Without polarization filter 20, polarization-changing material layer 4a, which may advantageously be transparent, does not visibly change the reflective properties of substrate 1, and therefore cannot be distinguished from the other portions of substrate 1. Preferably, a thickness of polarization-changing layer 4a is between 5 µm and 10 µm.

[0028] From the above explanation, it should be evident that the present disclosure is not limited to the case in which polarization-changing material layer 4a is formed on top of laser-engravable material 5. In other embodiments, polarization-changing material layer 4a may be formed on a substrate layer that is closer to second side S2 of substrate 1 than the substrate layer on which layer of laser-engravable material 5 is formed.

[0029] As previously mentioned, layer of laser-engravable material 5 may be a metallic material, preferably a mixture of a metallic material and an organic material, for example, with a ratio between 1:2 and 2:1. However, it will be appreciated that any appropriately configured metallic or non-metallic layer, in which a personalized image 3a can be laser-engraved, may be used as layer of laser-engravable material 5. As mentioned above, any appropriately configured metallic layer can be used, as long as at least a change in reflectivity, optionally in combination with a color-change can be obtained by irradiating layer of laser-engravable material 5 with laser light. As the formation of personalized images in such metallic layers is well-known, no further details will be mentioned herein.

[0030] In some embodiments, the metallic material of layer of laser-engravable material 5 includes metallic pigments, for example, one or more of Al, Ag, Au, Zn, Fe and Cu pigments.

[0031] Although Fig. 1 shows the case in which pattern 4b is disposed so as to overlap layer of laser-engravable material 5, more particular, image-forming region 3 defined by said layer, in other embodiments, as shown in Fig. 5, image-forming region 2 may include a portion of substrate 1 configured to have a primary portrait of a holder of security document 10 laser-engraved in the same. Again, as shown in Fig. 5, after formation of personalized image 2a in image-forming region 2, and upon providing polarization filter 20, both personalized image 2a and pattern 4b overlapping the same can be observed. Without polarization filter 20, pattern 4b will disappear.

[0032] In this manner, also a primary portrait forming personalized image 2a can be additionally secured by providing selectively visible pattern 4b. Similar to what has been described above for layer of laser-engravable material 5, polarization-changing material layer 4a may be provided above or below the substrate layer in which personalized image 2a is formed. This is because, even if polarization-changing material layer 4a is formed on top of the substrate layer in which personalized image 2a is to be engraved, polarization-changing material layer 4a is formed from a material which is not laser-reactive, i.e., which does not alter its appearance, for example, from a substantially transparent appearance upon irradiation with laser light, at least as long as the laser power that is used to form personalized image 2a does not exceed a specific threshold. For example, as will be described in more detail in the following, the laser that is used to form personalized images 2a, 3a may be configured such that a laser power of the same does not exceed a laser power of 30 W, preferably 20 W.

[0033] In other embodiments, as shown in Fig. 6, polarization-changing material layer 4a, more particularly, pattern 4b may be provided over the entirety of substrate 1, for example, overlapping both image forming region 2 and image forming region 3. This is indicated by a dashed line in Fig. 3. In this manner, as shown in Fig. 6, both a primary portrait and a secondary portrait can be secured with the additional selectively visible pattern 4b. It should be noted that polarization filter 20 is omitted in Fig. 6 for the sake of clarity, and that Fig. 6 shows personalizable security document 10 prior to personalization of the same.

[0034] In other exemplary embodiments, as shown in Fig. 7, security feature 4 further includes a fluorescent material layer 6 (indicated by dotted lines in Fig. 3) configured to emit visible light upon irradiation with light of a first wavelength in the ultraviolet (UV) or infrared (IR) wavelength range. In particular, fluorescent material layer 6 forms a complementary pattern 6a that is complementary to pattern 4b and combines with the same to form an image or text 7 that is visible when substrate 1 is viewed from first side S1 both under white light and under light of the first wavelength. Here, fluorescent material layer 6 may be provided on substrate 1 in any appropriate manner, for example, on topmost substrate layer 31, as shown in Fig. 3, or on any other substrate layer of the plurality of substrate layers 31-35, as long as the light emitted by fluorescent material layer 6 is visible from first side S1 of substrate 1 upon illumination of the same. As shown in Fig. 7, an additional layer of security is provided in such a case, because, for example, the text formed by pattern 4b and complementary pattern 6a forms a continuous pattern, and if one of the two features is tampered with, this continuity may be destroyed (for example, the different patterns may be offset with respect to each other). Of course, it will be immediately recognized that this can also be achieved if patterns 4b, 6a do not form a text pattern, but instead form a predetermined image or abstract pattern.

[0035] In the above-described embodiments, the presence of polarization-changing material layer 4a results in that pattern 4b is selectively visible when polarization filter 20 is provided. However, at least in embodiments in which pattern 4b is provided so as to overlap layer of laser-engravable material 5, which includes a metallic material, it has been found that pattern 4b can also be observed when substrate 1 is viewed against white light from first side S1. In this manner, pattern 5b can selectively be made visible by changing the observation mode, without the need for providing polarization filter 20.

[0036] This is an additional advantage that can be achieved with the configuration in which a combination of a polarization-changing material layer or pattern and a metallic laser-engravable material is used. Of course, the visibility in transmission requires that the underlying substrate layers are at least partially transparent, such that sufficient light reaches layer of laser-engravable material 5 and polarization-changing material layer 4a when substrate 1 is viewed against white light. At least in configurations in which layer of laser-engravable material 5 and polarization-changing material layer 4a form part of a security feature that extends through substrate 1, such as a transparent window formed in a white polycarbonate substrate, this can be assured.

[0037] The integrity of a personalized security document 10 including the above-described security feature 4 can be verified by providing an appropriate device 100 that is shown in Fig. 8. Device 100 may be a portable device such as a mobile phone, a tablet computer or the like. Device 100 includes a light source 102 configured to emit light in the visible range towards security document 10. Further, device 100 includes a camera 104 configured to capture an image of a portion of security document 10 including security feature 4. Any commonly available mobile phone generally includes such a light source and a camera.

[0038] Additionally, device 100 includes a polarization filter 106 covering light source 102 and camera 104. In some embodiments, an appropriate adapter or cover may be mounted to a mobile phone in a known manner in order to cover the light source and the camera of the same.

[0039] Device 100 further includes a display 108 and a controller 110. Controller 110 may be any appropriate controller, such as a commonly used microprocessor or microcomputer of a mobile phone, a tablet computer, or any other computing device. Controller 110 may be configured by appropriate software, for example, by installing an app or the like on a mobile phone, to perform the functions of controlling light source 102 to emit light towards security document 10 via polarization filter 106, control camera 104 to capture an image of security document 10 while emitting the light towards security document 10, and, optionally, analyzing the captured image to determine whether predetermined pattern 4b included in security feature 4 is present or not.

[0040] As explained above, if predetermined pattern 4b is present, said pattern 4b is visible in the image captured by camera 104 while irradiating polarized light. Controller 110 can use any known image recognition technique in order to determine whether predetermined pattern 4b, which may be stored in advance in a memory of device 100, is present or not. The details of such a verification using appropriately configured software are known to the skilled person, such that they will be omitted herein.

[0041] In response to the determination whether predetermined pattern 4b is present or not, controller 110 may be configured to display an indicator 112 indicating a result of the determination on display 10. For example, controller 110 may be configured to display both the pattern 4b that is recognized in the captured image and indicator 112 indicating a positive result on display 108. Alternatively, controller 110 may be configured to display only one of pattern 4b and indicator 112. In some embodiments, image recognition may not be performed, and only the captured image including the pattern 4b may be displayed and verified by an operator.

[0042] Using device 100, an operator, for example, security personnel or the like, may easily verify the integrity of security document 10 using an appropriately configured mobile phone or another dedicated device.

[0043] In order to facilitate the verification of security feature 4, device 100 may further comprise a positioning unit 120 configured to position security document 10 in a predetermined verification position with respect to camera 104. In this manner, it can be assured that camera 104 can reliably capture an image of the region of security document 1, in which pattern 4b is formed (or should be formed if document 10 has not been tampered with). In particular, positioning unit 120 may arrange security document 10 at a predetermined distance, in a predetermined orientation, and the like with respect to camera 104.

[0044] It will be appreciated that, after manufacturing, security document 10 may be a personalizable security document. In other words, personalized images 2a, 3a may not yet be present, such that security document 10 is not yet personalized (see Fig. 1). Generally, such a personalization will be carried out by the respective issuers of the security documents, for example, passports, identification cards, driver's licenses or the like, as will be described in more detail below.Industrial applicability

[0045] With the above-described configurations, an additional layer of security for a personalizable security document 10 can be provided, by combining a hidden pattern 4b with a personalized image formed in an image-forming region 2, 3 of security document 10. Additionally, a practical device for easily verifying the presence of pattern 4b is provided. For example, any commonly used mobile phone or tablet computer can be provisioned with an appropriate polarization filter 20, and can be used to determine whether pattern 4b is present or not.

[0046] Personalizable security document 10 may be formed in any appropriate manner, as long as polarization-changing material layer 4a is provided such that it overlaps at least in part with one of image-forming regions 2, 3. For example, as described above, personalizable security document 10 may be formed by laminating a plurality of substrate layers 31-35 in a known manner, where polarization-changing material layer 4a can be applied onto one of substrate layers 31-35 prior to lamination in a known manner, for example, by screen printing or the like. In some embodiments, layer of laser-engravable material 5 may be provided on a different one of substrate layers 31-35 prior to lamination, and may be aligned with polarization-changing material layer 4a during lamination.

[0047] A method of personalizing personalizable security document 10 includes the steps of providing a personalizable security document 10 in accordance with the present disclosure, and laser-engraving a personalized image 2a, 3a in image-forming region 2, 3 by varying one or more laser parameters.

[0048] Exemplary laser parameters that are used to engrave personalized image 3a are a laser wavelength between 530 nm and 1060 nm, a laser speed between 100 mm / s and 4000 mm / s, a laser repetition rate between 50 kHz and 100 kHz, and a laser power of less than 30 W, preferably less than 20 W.

[0049] It will be appreciated that the foregoing description provides examples of the disclosed systems and methods. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the general disclosure.

[0050] Recitation of ranges of values herein are merely intended to serve as a shorthand method for referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All method steps described herein can be performed in any suitable order, unless otherwise indicated or clearly contradicted by the context.

[0051] Although the preferred embodiments of the present disclosure have been described herein, improvements and modifications may be incorporated without departing from the scope of the following claims.

Claims

1. A personalizable security document (10) comprising: - a substrate (1) having a first side (S1) and a second side (S2) opposite to the first side in a thickness direction (d) of the substrate (1); - an image-forming region (2, 3) provided in the substrate (1) and configured to have a personalized image (2a, 3a) laser-engraved in the same from the first side (S1); and - a security feature (4) provided in the substrate (1), the security feature (4) including a polarization-changing material layer (4a) configured to change a polarization of light passing through the same, the polarization-changing material layer (4a) forming a pattern (4b) overlapping at least in part the image-forming region (2, 3), - wherein the pattern (4b) is not visible when the substrate (1) is viewed from the first side (S1) under white light in reflection, and becomes visible when the substrate (1) is viewed from the first side (S1) under white light through a polarization filter (20).

2. The security document of claim 1, wherein the security feature (4) further includes a layer of laser-engravable material (5) embedded in the substrate (1) and forming the image-forming region (3), the layer of laser-engravable material (5) exhibiting at least one of a change in reflectivity and a color-change upon irradiation with laser light from the first side (S1).

3. The security document of claim 2, wherein the layer of laser-engravable material (5) includes a metallic material, preferably a mixture of a metallic material and an organic material, more preferably with a ratio between 1:2 and 2:1.

4. The security document of claim 3, wherein the metallic material includes metallic pigments, for example, one or more of Al, Ag, Au, Zn, Fe and Cu pigments.

5. The security document of any one of claims 2 to 4, wherein the layer of laser-engravable material (5) is configured to have a secondary portrait, preferably a negative portrait, of a holder of the security document (10) laser-engraved in the same.

6. The security document of any one of claims 2 to 4, wherein the substrate (1) includes a plurality of substrate layers (31, 32, 33, 34, 35), and the polarization-changing material layer (4a) and the layer of laser-engravable material (5) are formed on different ones of the plurality of substrate layers (31, 32, 33, 34, 35).

7. The security document of claim 6, wherein the polarization-changing material layer (4a) is formed on a first substrate layer (32) closer to the first side (S1) of the substrate (1) than a second substrate layer (33) on which the layer of laser-engravable material (5) is formed.

8. The security document of any one of claims 1 to 7, wherein the image-forming region (2) includes a portion of the substrate (1) configured to have a primary portrait of a holder of the security document (10) laser-engraved in the same.

9. The security document of any one of claims 1 to 8, wherein the security feature (4) further includes a fluorescent material layer (6) configured to emit visible light upon irradiation with light of a first wavelength in the ultraviolet (UV) or infrared (IR) wavelength range, the fluorescent material layer (6) forming a complementary pattern (6a) that is complementary to the pattern (4b) and combines with the same to form an image or text (7) that is visible when the substrate (1) is viewed from the first side (S1) both under white light and under light of the first wavelength.

10. The security document of any one of claims 1 to 9, wherein the polarization-changing material layer (4a) is configured as an ink layer printed onto a substrate layer (32) of the substrate (1), preferably by screen printing or offset printing.

11. The security document of any one of claims 1 to 10, wherein the polarization-changing material layer (4a) includes liquid crystal particles.

12. The security document of any one of claims 1 to 11, wherein the pattern (4b) is visible when the substrate (1) is viewed against white light from the first side (S1).

13. A method of personalizing a security document (10), comprising: - providing a personalizable security document (10) in accordance with any one of claims 1 to 12; and - laser engraving a personalized image (2a, 3a) in the image-forming region (2, 3) by varying one or more laser parameters, preferably, wherein a laser power is less than 30 W, more preferably less than 20 W.

14. A device (100) for verifying a security feature (4) of a personalized security document (10), the security feature (4) including a polarization-changing material layer (4a) configured to change a polarization of light passing through the same, the device comprising: - a light source (102) configured to emit light in the visible range towards the security document (10); - a camera (104) configured to capture an image of a portion of the security document (10) including the security feature (4); - a polarization filter (106) covering the light source (102) and the camera (104); - a display (108); and - a controller (110) configured to: control the light source (102) to emit light towards the security document (10) via the polarization filter (106); control the camera (104) to capture an image of the security document (10) while emitting the light towards the security document (10); optionally, analyze the captured image to determine whether a predetermined pattern (4b) included in the security feature (4) is present or not; and display at least one of the observed pattern (4b) and an indicator (112) indicating a result of the determination on the display (108).

15. The device of claim 14, further comprising a positioning unit (120) configured to position the security document (10) in a predetermined verification position with respect to the camera (104).

Images