US-20260127904-A1 - DOCUMENT AUTHENTICATION BASED ON MODIFIED FONT DETECTION

US20260127904A1US 20260127904 A1US20260127904 A1US 20260127904A1US-20260127904-A1

Abstract

It is disclosed a method for authenticating a document (D), the document including a plurality of text fields, wherein an authentic document comprises, among the plurality of text fields, a plurality of characters printed according to a reference font, and at least one character, of determined location, being printed according to a font which is modified with respect to the reference font, the method comprising: receiving an image of the document to be authenticated, extracting, from the image, a region of interest including the character of determined location, assessing discrepancies between the character included in the extracted region of interest and a model character, and determining whether or not the document is authentic based on the assessed discrepancies.

Inventors

Rein-Lien Hsu
Brian Martin

Assignees

IDEMIA PUBLIC SECURITY FRANCE

Dates

Publication Date: 20260507
Application Date: 20251001
Priority Date: 20241105

Claims (12)

1 . A computer-implemented method for authenticating a document, the document including a plurality of text fields, wherein an authentic document comprises, among the plurality of text fields, a plurality of characters printed according to a reference font, and at least one character, of determined location, being printed according to a font which is modified with respect to the reference font, the method comprising: receiving an image of the document to be authenticated, extracting, from the image, a region of interest including the character of determined location, assessing discrepancies between the character included in the extracted region of interest and a model character, and determining whether or not the document is authentic based on the assessed discrepancies.
2 . The method according to claim 1 , wherein the model character is a reference template of the character printed according to the reference font or according to the modified font, and assessing discrepancies between the character included in the extracted region of interest and the reference template comprises computing difference in intensities between the two characters.
3 . The method according to claim 2 , wherein determining whether or not the document is authentic is based on detection of intensity discrepancies or on the locations of intensity discrepancies.
4 . The method according to claim 2 , wherein the model character is a reference template of the character printed according to the reference font, and assessing discrepancies between the character included in the extracted region of interest and the reference template further comprises determining locations of extrema of the intensity difference between the two characters, and comparing the determined locations of the extrema with reference locations of the differences.
5 . The method according to claim 4 , wherein the document is determined to be authentic when a distance between the determined locations of the difference extrema and the reference locations is below a determined threshold.
6 . The method according to claim 1 , wherein extracting a region of interest including a character comprises extracting a patch of the image including the character, normalizing the intensity of the patch, extracting and optionally resizing a bounding box of the character, the extracted bounding box forming the region of interest.
7 . The method according to claim 1 , wherein the character model is a reference template of the character printed according to the reference font.
8 . The method according to claim 1 , wherein the document includes a plurality of static text fields, and the character printed according to the modified font is located within one of the static text fields.
9 . The method according to claim 7 , wherein an authentic document comprises at least two occurrences of the same character, wherein at least a first occurrence of the character is printed according to the modified font, and at least a second occurrence of the character is printed according to a reference font, and the method further comprises acquiring the reference template from the document to be authenticated, at a location corresponding to the second occurrence of the character, and acquiring the reference template from the image includes extracting a patch comprising the character according to the reference font from the image, normalizing the intensity of the patch and extracting a bounding box (tightened around contours) of the character, the extracted bounding box forming the reference template.
10 . A computer-implemented method of generating a database for document authentication, comprising adding to the database, for each of a plurality of document types, data descriptors of at least one character model and of at least one character printed according to a modified font with respect to a reference font, including at least a determined location, in an authentic document, of the character printed according to the modified font.
11 . A document authentication system, comprising at least an image sensor adapted to acquire an image of a document to be authenticated, a database storing, for each of a plurality of document types, data descriptors of the model character and of the character printed according to the modified font, including at least a determined location, in an authentic document, of the character according to the modified font, and a computer configured to receive images acquired by the image sensor and to implement the method according to claim 1 .
12 . The document authentication system according to claim 11 , wherein the data descriptors further include at least one of: a reference template of the character printed according to the modified font or printed according to the reference font, An expected location of each discrepancy between the model character and the character printed according to the modified font. a height, width, or aspect ratio of the model character, expected locations of extrema of intensity discrepancies between the character according to the modified font and the character according to the reference font, threshold values regarding intensity discrepancies, or locations thereof, between a character and a reference template thereof.

Description

TECHNICAL FIELD This disclosure pertains to the field of document authentication and fraud detection in documents, such as ID documents. BACKGROUND ART Identity documents are conventionally secured by incorporating a variety of security features. These features aim at ensuring authenticity, integrity and protection against fraud or tampering of the documents, and thus distinguishing an authentic document from a fraudulent one. During identity control, the presence and integrity of the security features is checked in order to authenticate the document. Security features may include for instance holograms, watermarks, microprinting, UV ink, etc. A document, in particular an ID document, generally comprises both static text fields and variable text fields. Static text fields include text that does not vary according to the owner of the document, whereas variable text fields include text that varies according to the owner, also referred to as Personal Identifiable Information. Typically, a static text field does not contain any personal or document-related data, but may indicate the type of personal data that fills a neighboring variable text fields. In the case of an ID document, a static text field may include words such as “Name”, “Surname”, “Date of birth”, “Date of delivery”, “Signature”, etc. The static text fields may also include text identifying the document type and issuing authority. Some documents may include dedicated fonts as a security feature, referred to as modified font. The modified font may have the same font style as the one used for the surrounding static texts—also called reference font, the modified font being different but close to the reference font (with for example a slight modification brought to the reference font) or have a different font style. The changes between the first font and the modified font may be subtle, requiring careful and slow examination when the authentication of the document is performed by a human operator. There is therefore a need for a fast and reliable solution for automatic examination of such a security feature. It is known from the [Lu, 2020] a method for detecting forged text in a document that classifies a document as fraudulent or authentic based on a Discrete Cosine Transform (DCT) of the document followed by an inverse DCT applied to the positive and negative coefficients of the DCT. This method does not enable specifically detecting a tampered font but instead aims to find any change in general, not specific to font style change as it relies on an overall change in the distribution of intensity of the pixels of a document which has been tempered. SUMMARY This disclosure aims at improving the situation. In particular, one aim of the present disclosure is to provide a fast and reliable solution for automatically authenticating a document based on the verification of a modified font. Another aim of the present disclosure is to provide a method that can accommodate various types of modified fonts, including various characters and various types of modifications to the fonts. Accordingly, a computer-implemented method for authenticating a document is disclosed, the document including a plurality of text fields, wherein an authentic document comprises, among the plurality of text fields, a plurality of characters printed according to a reference font, and at least one character, of determined location, being printed according to a font which is modified with respect to the reference font, the method comprising: receiving an image of the document to be authenticated,extracting, from the image, a region of interest including the character of determined location,assessing discrepancies between the character included in the extracted region of interest and a model character, anddetermining whether or not the document is authentic based on the assessed discrepancies. In embodiments, the model character is a reference template of the character printed according to the reference font or according to the modified font, and assessing discrepancies between the character included in the extracted region of interest and the reference template comprises computing difference in intensities between the two characters. In embodiments, determining whether or not the document is authentic is based on detection of intensity discrepancies or on the locations of intensity discrepancies. In one embodiment, the model character is a reference template of the character printed according to the reference font, and assessing discrepancies between the character included in the extracted region of interest and the reference template further comprises determining locations of extrema of the intensity difference between the two characters, and comparing the determined locations of the extrema with reference locations of the differences. According to this embodiment, the document is determined to be authentic when a distance between the determined locations of the difference extrema and