| 摘要 |
A method and system for printing an original image which is protected against copying or alteration, such as a postal indicium, and for determining if that image has been altered. The image includes a copy detection feature and coded information linked to the copy detection feature. Altered images are detected by testing to determine if the link between the copy detection feature and the coded information if fact exists. The copy detection feature and the coded information can be linked by: 1) generating said copy detection feature as a pseudorandom function of said coded information; identifying a type of printer corresponding to said printer; and incorporating information identifying said type of printer into said image; or 2) creating a robust descriptor of said copy detection feature; and incorporating said descriptor into said coded information; or 3) creating a robust descriptor of said copy detection feature; and incorporating said descriptor into said coded information, and modifying said copy detection feature as a pseudorandom function of said coded information; or 4) generating said copy detection feature as a pseudorandom function of said coded information; creating a robust descriptor of said copy detection feature; and incorporating said descriptor into said coded information.
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