Method of authenticating a printed document

Patent metadata

Field	Value
Publication number	US-9349237-B2
Application number	US-201213730743-A
Country	US
Kind code	B2
Filing date	Dec 28, 2012
Priority date	Dec 28, 2012
Publication date	May 24, 2016
Grant date	May 24, 2016

Abstract

A method for authenticating a printed document which carries barcode that encode authentication data, including word bounding boxes for each word in the original document image and data for reconstructing the original image. The printed document is scanned to generate a target document image, which is then segmented into text words. The word bounding boxes of the original and target document images are used to align the target document image. Then, each word in the original document image is compared to corresponding words in the target document image using word difference map and Hausdorff distance between them. Symbols of the original document image are further compared to corresponding symbols in the target document image using feature comparison, symbol difference map and Hausdorff distance comparison, and point matching. These various comparison results can identify alterations in the target document with respect to the original document, which can be visualized.

First claim

What is claimed is:

1. A method for authenticating a printed document, the printed document carrying barcode which encodes compressed image data representing a binary original document image, the method comprising:
(a) obtaining an image representing the printed document;
(b) separating the image into a target document image and the barcode;
(c) decoding the barcode and decompressing the compressed image data therein to obtain the original document image;
(d) binarizing the target document image;
(e) aligning the target document image with respect to the original document image;
(f) comparing each word in the original document image with a corresponding word in the target document image to detect any differences, comprising:
(f1) for each word of the original document image obtained in step (c), finding the corresponding word of the target document image;
(f2) generating a difference map and calculating a Hausdorff distance between each word of the original and the corresponding word of the target document image, and comparing the difference map and the Hausdorff distance to determine whether the corresponding words of the original and target document images are different;
(f3) if the words of the original and target document images are not determined to be different in step (f2), identifying one or more candidate symbols in the word of the original document image and corresponding candidate symbols in the target document image;
(f4) comparing image features of each candidate symbol of the original document image identified in step (f3) with image features of the corresponding candidate symbol of the target document image to determine whether any of the corresponding candidate symbols of the original and the target document images are different;
(f5) if the corresponding symbols of the original and target document images are not determined to be different in step (f4), generating a difference map and calculating a Hausdorff distance between each candidate symbol of the original document image and the corresponding candidate symbol of the target document image, and comparing the difference map and the Hausdorff distance to determine whether any of the corresponding candidate symbols of the original and target document images are different; and
(f6) if the corresponding symbols of the original and target document images are not determined to be different in step (f5), comparing shapes of each candidate symbol of the original document image and the corresponding candidate symbol of the target document image using a point matching method to determine whether any of the corresponding candidate symbols of the original and target document images are different; and

(g) visualizing the differences detected in step (f).

2. The method of claim 1 ,
wherein the barcode further encodes a plurality of original word bounding boxes each corresponding to a word in the original document, wherein step (c) further includes obtaining the plurality of original word bounding boxes from the barcode, and
wherein step (e) comprises:
(e1) segmenting the target document image into words to obtain target word bounding boxes corresponding to words in the target document image;
(e2) matching at least some of the plurality of original word bounding boxes obtained in step (c) and at least some of the target word bounding boxes obtained in step (e1) to align the target document mage;
(e3) based on the alignment obtained in step (e2), further aligning the target document image using the target document image and the original document image.

3. The method of claim 2 , wherein the barcode further encodes a plurality of original text line bounding boxes each corresponding to a line of text in the original document image, wherein step (c) further includes obtaining the plurality of original text line bounding boxes from the barcode, and
wherein step (e1) further includes segmenting the target document image into lines of text to obtain target text line bounding boxes corresponding to lines of text in the target document image, and
wherein step (e2) further includes matching at least some of the plurality of original text line bounding boxes obtained in step (c) and at least some of the target text line bounding boxes obtained in step (e1) to align the target document image.

4. The method of claim 2 , wherein the step (f2) uses a RANSAC (RANdom SAmple Consensus) method.

5. The method of claim 1 , wherein step (a) comprises scanning the printed document to generate a scanned image and pre-processing the scanned image including de-noising, de-skewing, and/or correction of perspective distortions.

6. The method of claim 1 , wherein in step (f4), the image features include zoning profiles, side profiles, topology statistics, and low-order image moments.

7. The method of claim 1 , wherein step (g) includes displaying or printing the original or target document image with indications that indicate any words of the original document image or the corresponding words of the target document image that are determined to be different in step (f2) and any candidate symbols of the original document image or the corresponding candidate symbols of the target document image that are determined to be different in steps (f4), (f5) and (f6).

8. A computer program product comprising a computer usable non-transitory medium having a computer readable program code embedded therein for controlling a data processing apparatus, the computer readable program code configured to cause the data processing apparatus to execute a process for authenticating a printed document, the printed document carrying barcode which encodes compressed image data representing a binary original document image, the process comprising:
(a) obtaining an image representing the printed document;
(b) separating the image into a target document image and the barcode;
(c) decoding the barcode and decompressing the compressed image data therein to obtain the original document image;
(d) binarizing the target document image;
(e) aligning the target document image with respect to the original document image;
(f) comparing each word in the original document image with a corresponding word in the target document image to detect any differences, comprising:
(f1) for each word of the original document image obtained in step (c), finding the corresponding word of the target document image;
(f2) generating a difference map and calculating a Hausdorff distance between each word of the original and the corresponding word of the target document image, and comparing the difference map and the Hausdorff distance to determine whether the corresponding words of the original and target document images are different;
(f3) if the words of the original and target document images are not determined to be different in step (f2), identifying one or more candidate symbols in the word of the original document image and corresponding candidate symbols in the target document image;
(f4) comparing image features of each candidate symbol of the original document image identified in step (f3) with image features of the corresponding candidate symbol of the target document image to determine whether any of the corresponding candidate symbols of the original and the target document images are different;
(f5) if the corresponding symbols of the original and target document images are not determined to be different in step (f4), generating a difference map and calculating a Hausdorff distance between each candidate symbol of the original document image and the corresponding candidate symbol of the target document image, and comparing the difference map and the Hausdorff distance to determine whether any of the corresponding candidate symbols of the original

Assignees

• Tian Yibin
• Ming Wei
• Konica Minolta Lab Usa Inc

Inventors

• Tian Yibin
• Ming Wei

Classifications

• G07D7/00

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• G07D7/2058 Primary

  Physics · mapped topic

• G07D7/206 Primary

  Matching template patterns · CPC title

• B42D15/00 Primary

  Printed matter of special format or style not otherwise provided for · CPC title