Patent ID: 8000528

Claim:
A method implemented in a data processing apparatus for authenticating a target document image by comparing the target document image with an original document image, comprising: comparing the target document image with the original document image at a first level, including: (a) segmenting the target document image into a plurality of first-level units; (b) segmenting the original document image into a plurality of first-level units; (c) comparing the plurality of first-level units in the target document image with the plurality of first-level units in the original document image to detect alterations in the target document image; and if no alteration is detected in step (c), comparing the target document image with the original document image at a second level, including: (d) segmenting the target document image into a plurality of second-level units, wherein the second-level units are smaller than the first-level units; (e) segmenting the original document image into a plurality of second-level units, wherein the second-level units are smaller than the first-level units; and (f) comparing the plurality of second-level units in the target document image with the plurality of second-level units in the original document image to detect alterations in the target document image.