Self-verifiable paper documents and automatic content verification

摘要

This report describes a method for the creation and automatic content verification of low-cost self-verifiable paper documents. The image of an original document is decomposed to symbol templates and their corresponding locations. The resulting data is further compressed and encrypted, and encoded in custom designed high-capacity color barcodes. The original image and barcodes are printed on the same paper to form a self-verifiable authentic document. During content verification, the paper document is scanned to obtain the barcodes and target image. The original image is reconstructed from data extracted from the barcodes, which is then registered with and compared to the target image. The verification is carried out hierarchically from the entire image down to word and symbol levels. For symbol level comparison, multiple types of features and shape matching are utilized in a cascade. The proposed verification method is inexpensive, robust and fast. Evaluation on 216 character tables and 102 real documents achieved greater than 99% alteration detection rate and less than 1% false positives at the word/symbol level.