Research On Semi-fragile Watermarking Technique For Digital Image

After giving a brief overview of the digital image authenticating, this thesis focous on the image authentication based on semi-fragile watermarking, and makes some researches on this.At the beginning, an improved algorithm is proposed for resist a special counterfeiting attack on an algorithm. Then, to solve a problem that most existing algorithm can not distinguish tamper styles, a novel semi-fragile watermarking algorithm that can resist JPEG compression is presented. Finally, a semi-fragile watermarking algorithm can resist the domain transform is proposed, which most algorithms can not resist. The main contents are as follows:Firstly, a counterfeiting attack is proposed and realized, based on the analysis of a current watermark algorithm, aimed at the algorithm security. So a high-security authentication algorithm for JPEG image is presented. This algorithm realize the protection of the content and the watermark by using both the watermark generation coefficients and watermark embedded coefficients to generate the watermark. Theoretical analysis and experimental results show that the proposed algorithm can resist collage attack efficiently and have a smaller false negative probability than the existing algorithm.Secondly, in most existing JPEG image authentication algorithm, it is impossible to distinguish tamper styles. So taking advantage of the invariance of JPEG compression, a JPEG image authentication algorithm with distinguishing of tampers based on multi-watermarking scheme is proposed, in which the dual-watermarking and the smallest block correlating are exploited to realize the watermark generation and the watermark embedding, so as to distinguish the tamper styles and to locate the tamper region. This algorithm has accurate locating and efficient distinguishing of tampers, as well as better JPEG compression resistance and lower false positive probability. Experimental results show that the algorithm is effective.In addition, for most existing semi-fragile watermarking, there exist some problems in the performance in terms of anti-JPEG compression. Therefore, this paper brings up a novel algorithm which can resist JPEG compression. The proposed algorithm constructs the compensation matrices of the pixel values by matrix operation, of which the JPEG coefficients are embedded watermark in, so that the watermark will be same under domain transform. Theoretical analysis and experimental results show that this algorithm can resist the domain transform and re-quantizaion of the JPEG compression .Finally, conclusions are drawn, and the further researches are put forward.