Semi-fragile watermarking scheme with discriminating general tampering from collage attack

A semi-fragile watermarking scheme is proposed to discriminate general tampering and collage attack in this paper. Five bits watermark data of each block generated are divided into the general tampering watermark (GTW) and collage attack watermark (CAW), which are embedded in the same block and the other blocks to discriminate general tampering and collage attack. The general tampered regions are obtained by the GTW data, and used to define a new collage identification parameter (CIP) combined with the consistency mark of collage attack. If the CIP is less than the given threshold, there are collaged regions in the test image and the CAW data is used to localize the collaged region. This work also discusses the selection of threshold of CIP. Experimental results show that the proposed algorithm improves the tamper detection performance compared to the existing semi-fragile watermarking algorithms and has the ability to discriminate general tampering from collage attack.