Patent Description:
In the area of counterfeiting, the use of non-original documents can lead to serious fraud problems. The use of paper copies of original confidential documents is the main channel of information leakage. The document replication of financial documents, either by photocopying or by scanning and subsequent printing, contributes to generating fraud in payments that are made.

In most cases, the document verification process is carried out manually. This entails a problem of high cost, due to personnel dedicated to manually analysing documents, and the possibility of human errors in the identification due to the subjectivity of the test.

Currently there are also photocopy identification systems that use the incorporation of semi-fragile watermarks in original documents. Said watermarks are lost when the document is replicated by means of the photocopying system. In this way, the identification of the document originality is conditioned only by the existence or absence of the mark. However, the loss of the digital watermark prevents maintaining the traceability of the document throughout its entire useful life, and it results in a loss of data and additional useful information included in the digital watermark itself.

Patent document <CIT> discloses a method for authenticating a media signal with an embedded digital watermark, wherein a metric is calculated and then embedded in the media signal. To detect a potential alteration, a detector computes the metric for a potentially corrupted version of the embedded media signal. The detector then compares its computed metric to the embedded metric to detect whether the alteration has occurred.

The present invention solves the problem of fraud associated with document replication by photocopying and/or scanning and printing, enabling the automatic and instantaneous identification of manipulated documents, and thus preventing the use and acceptance of non-original documents (for example, used for payments, in the case of financial documents).

The invention relates to a system and method for automatic identification of photocopied documents according to the appended claims. In the context of the present invention, the term "photocopied documents" includes photocopies of an original document and documents obtained by scanning an original document and the subsequent printing thereof.

The present invention enables photocopies to be automatically identified by analysing the parameters of the digital watermark and incorporating digital watermarks with ultraviolet ink (UV mark) as a second verification layer. Unlike current solutions, the present invention identifies a photocopied document without losing the digital watermark, and therefore maintains the traceability of the document throughout its entire useful life and the benefits that the digital watermark provides with respect to including data and information additional to what is visible in the document.

The implementation of the solution enables an original document to be instantly differentiated from a photocopied one. In addition, it adds value by automating the document verification process, which is reflected in the reduction of costs related to personnel dedicated to manually analysing documents, the elimination of errors due to human subjectivity, and the increase in efficiency, among others.

The method for automatic identification of photocopied documents according to claim <NUM> comprises the following steps:.

Obtaining the calibration identifier comprises, according to a preferred embodiment, decoding a digital watermark embedded in the image, obtaining a mark identifier, wherein the calibration identifier is the mark identifier. Alternatively, the calibration identifier can be other data included in the marked printed document itself which enables the calibration carried out to obtain a calibration identifier to be identified; for example, in a check the calibration identifier may be the check batch number. In this way, in the database the batch number can be correlated with the calibration carried out, obtaining the calibration threshold associated with said batch.

The photocopy identifier of the present invention is an automatic system that, by means of reading software installed in an image capturing device (scanner, mobile phone camera, etc.), is capable of recognising whether a document is an original or a copy (photocopied and/or scanned and printed, for example). The solution can be integrated with other document authenticity systems as an extra verification measure or it can work on its own in a device with reading capacity (scanner, mobile phone camera, etc.) when the aim is solely to identify a photocopy. The system works due to the encryption of digital watermarks at the time of printing the original document and/or the digital generation thereof. The reading software for the digital watermark is capable of detecting when the digital watermark is altered due to photocopying processes, thus alerting the user that the document they have is not the original.

The printing equipment accesses digital watermark embedding software and calibration software after capturing the image. The embedding software marks the documents to be printed and keeps track of which digital watermarks have been used. The calibration software is used when the printing parameters are changed to calibrate the system, with a minimum of five documents. In the event of requiring highly accurate detection, it is advisable to carry out a calibration for each batch of documents.

At the document reception/verification points, the reading software for digital watermarks is implemented by means of a scanner or by means of a mobile device (e.g., mobile phone). After scanning the documents, the software decrypts the embedded digital watermarks and verifies the parameters of the digital watermark, specifically a frequency analysis is performed on the image. This data is compared to that registered in the database at the time of calibration. By analysing and comparing these parameters, the system is able to automatically verify if they are within the threshold calculated at the time of calibration to determine whether it is an original or a photocopy. The software implemented in the scanner or in the mobile device generates a response that identifies whether the document being verified is a photocopy or an original document.

What follows is a very brief description of a series of drawings that aid in better understanding the invention, and which are expressly related to an embodiment of said invention that is presented by way of a non-limiting example of the same.

The present invention relates to a photocopy verification system based on an image frequency analysis, for identifying digital images that contain a digital watermark but have been exposed to a printing and digitisation process in order to obtain fraudulent copies of the same (photocopies and/or scanning and printing). In addition, to achieve a double verification of authenticity, there is the option of embedding a digital watermark with ultraviolet ink, UV mark, which, when analysing the document with a UV scanner and not finding the UV digital watermark, can identify the fraudulent copies.

The frequency being sought is the frequency at which the digital watermark saves the information. This frequency represents the number of pixels that the digital watermark uses to save information per unit of length. For example, in the event of having a digital watermark at a frequency of <NUM> in-<NUM>, it means that the digital watermark uses <NUM> pixels per inch to save the information. For such identification, a pattern analysis mechanism is used on the pixels of the image which comprises:.

<FIG> schematically represents the components involved in a system for automatic identification of photocopied documents 100a according to a possible embodiment. The system 100a comprises an image acquisition device <NUM> and a photocopied document identification device <NUM>. Both devices can be grouped into a verifying equipment <NUM>.

The image acquisition device <NUM> is responsible for capturing an image <NUM> of a marked printed document <NUM> to be verified. A data processing unit (<NUM>) of the photocopied document identification device <NUM> receives said image <NUM> and analyses it to determine whether the printed document is an original document <NUM> or a photocopied document <NUM>.

The photocopied document identification device <NUM> may be, by way of example, a computer or any device with image computing and analysis capabilities. The image acquisition device <NUM> can be a scanner or a camera. In the embodiment shown in <FIG>, both devices (<NUM>, <NUM>) are independent entities, which can be communicated by cable or wirelessly for sending and receiving the image <NUM>. Alternatively, the image acquisition device <NUM> may store the image <NUM> in a memory (on a memory stick, on a remote server hard disk, etc.) which will subsequently be accessed by the photocopied document identification device <NUM>.

<FIG> shows another embodiment of a system for automatic identification of photocopied documents 100b. In this embodiment, the image acquisition device <NUM> forms part of the photocopied document identification device <NUM>; in other words, said devices (<NUM>, <NUM>) are not independent entities. For example, the photocopied document identification device <NUM> can be a mobile device (e.g., tablet, smartphone) and the image acquisition device <NUM> can be a camera of said mobile device.

<FIG> represents a flow chart of a method for automatic identification of photocopied documents <NUM> according to a possible embodiment. The system (100a, 100b) for automatic identification of photocopied documents of <FIG> and <FIG> is configured to execute the steps of the method <NUM>. Particularly, the method <NUM> of <FIG> comprises the following steps:.

According to the embodiment of <FIG>, the method <NUM> may further comprise the step of converting <NUM> the frequency matrix <NUM> to a logarithmic scale, and binarising <NUM> the matrix converted to a logarithmic scale so that the matrix values above a certain binarisation threshold corresponds to maximum frequency values. The chosen binarisation threshold is preferably proportional to the matrix converted to a logarithmic scale (e.g., the selected binarisation threshold may be half the maximum value of the matrix). The method <NUM> may further comprise resizing <NUM> the image <NUM> to a certain size prior to applying <NUM> the discrete Fourier transform.

<FIG> schematically shows an embodiment of a system for automatic identification of photocopied documents <NUM> which includes, in addition to verifying equipment <NUM> according to an embodiment of any of the preceding figures, printing equipment <NUM> and a database <NUM>.

With respect to the printing equipment <NUM>, a digital watermark embedding device <NUM> has processing means configured to insert a digital watermark into a digital document <NUM> to obtain a marked digital document <NUM>. The digital watermark comprises at least one encoded mark identifier <NUM>. The digital watermark embedding device <NUM> stores the mark identifier <NUM> in the database <NUM>.

A printer <NUM> is responsible for printing the marked digital document <NUM>, obtaining one or more printed documents for calibration <NUM>. Calibration equipment <NUM> has a scanner <NUM>, responsible for carrying out a calibration scan of the printed documents for calibration <NUM>, and a control unit <NUM> (i.e., a data processing unit, such as for example a CPU) configured to limit the maximum marking frequency values obtained in the calibration scan to obtain a calibration threshold <NUM> and to store the calibration threshold <NUM> in the database <NUM>, associating it with the corresponding mark identifier <NUM> thereof.

The verifying equipment <NUM> receives a marked printed document <NUM> to be verified. The data processing unit <NUM> executes the corresponding steps of the method <NUM> previously described in <FIG>, recovering the mark identifier <NUM> embedded in the marked printed document <NUM>, searching <NUM> the database <NUM> to recover the calibration threshold <NUM> associated with said mark identifier <NUM>, and finally issuing a result of the verification <NUM>, wherein it is determined <NUM> whether the printed document is an original document <NUM> or a photocopied document <NUM>.

The digital watermark frequency analysis method, which comprises a diagnostic step and a previous calibration step, is explained in detail below, according to various preferred embodiments. The calibration step, carried out by the printing equipment <NUM>, comprises:.

Once the calibration step has been completed, by which the calibration threshold <NUM> is obtained which enables detecting whether the document to be verified is original or only a photocopied one, the diagnostic step on a marked printed document <NUM> can now be started to determine the veracity of the same. The diagnostic step, carried out by the verifying equipment <NUM> and explained in the flow diagram of <FIG>, comprises:.

Next, the embedding of the digital watermark in the digital document <NUM> is explained in detail, according to possible preferred embodiments. The digital watermark embedding device <NUM> comprises a data processing unit that executes a digital watermark embedding software, which enables the digital watermark to be inserted into the digital document <NUM> before printing. Using stenographic techniques and cryptography (using a digital watermark private key, a unique digital watermark numeric key for each document), the digital watermark embedding device <NUM> is able to hide a number of bits corresponding to the mark identifier <NUM> (usually <NUM> or <NUM> bits) on a digital image fulfilling the following requirements:.

The document is preferably printed using black toner, and it works as follows:.

In the event that a digital watermark with ultraviolet ink is embedded as an additional measure of authenticity verification, the implementation using ink only visible under ultraviolet light is as follows:.

The top layer containing the digital watermark is visually imperceptible.

With respect to the acquisition of the image <NUM> from the marked printed document <NUM> (initial step necessary to recover the <NUM> bits that have been encoded as the mark identifier), the image acquisition device <NUM> used may be a scanner or a camera.

In the case of using a scanner, the printed image is digitised on a physical medium and the reading algorithm is applied to the digital image to recover the mark identifier <NUM>. If it exists, the calibration parameters are searched in the database. In a first variant, the image is scanned under ultraviolet light and the ultraviolet mark is recovered. In a second variant, the document is scanned under visible light to recover the digital watermark and thus be able to search the calibration data (calibration threshold <NUM>) in the database <NUM>.

In the event of using a camera, the image exposed to the camera is digitised several times per second. A rectangular digital sub-image is obtained from the centre of the image. The reading algorithm is then applied to each sub-image until the mark identifier is recovered, at which time the digitisation stops until further intervention by the user. Once the mark identifier <NUM> has been obtained, the frequencies thereof can be analysed and the originality thereof determined. In a first variant, when scanning the image, ultraviolet light is applied to reveal an encoded image printed in ultraviolet ink. In a second variant, the document is scanned under visible light to recover the digital watermark and thus be able to search the calibration data in the database <NUM>.

Claim 1:
A method for automatic identification of photocopied documents, comprising:
capturing (<NUM>) an image (<NUM>) of a marked printed document (<NUM>);
obtaining, from the captured image (<NUM>), a calibration identifier;
recovering, by searching (<NUM>) a database (<NUM>), a calibration threshold (<NUM>) associated with the calibration identifier;
applying (<NUM>) a discrete Fourier transform to the image, obtaining a frequency matrix (<NUM>);
obtaining (<NUM>) at least one maximum frequency value (<NUM>) in the frequency matrix (<NUM>);
comparing (<NUM>) the at least one maximum frequency value (<NUM>) with the calibration threshold (<NUM>);
determining (<NUM>), on the basis of the comparison, if the marked printed document (<NUM>) is an original document (<NUM>) or a photocopied document (<NUM>);
wherein the calibration threshold is x ± No, wherein x is the mean and σ is the standard deviation of the maximum frequency values obtained in a calibration scan, and the value of N determines the amplitude of the calibration threshold.