Image Authentication Based On Digital Watermarking And Its Key Issues

The security issues about multimedia information have become increasingly prominent with the rapid development of network technology. Digital image is a representative multimedia with huge data, high redundancy and various formats. Traditional digital signature technology has great limitations in protecting multimedia information. The new digital watermarking technology not only can authenticate the image integrity, but also can distinguish the malicious alters from legal manipulations, and localize the image alters, which offers an effective solution for image authentication in internet environment. In recent years, the image authentication based on digital watermaking becomes a hot topic in information security.This thesis is focused on the several key issues of image authentication watermarking. We have proposed some novel algorithms and models in fragile watermarking, semi-fragile watermarking, image block-dividing watermarking and binary image authentication watermarking. The main research work and innovations are as follows:To solve the key issue, the conflict between the watermark security and the localization accuracy, in image authentication watermarking technology, we have proposed a circural block-dependent structure and a divergent block-dependent structure. Based on the proposed two structures, we have proposed a fragile watermarking algorithm, a JPEG semi-fragile watermarking algorithm and a DWT semi-fragile watermarking algorithm. The advantage of the DWT semi-fragile watermarking algorithm is that the JPEG and JPEG2000 selective authentication can be achieved. Experimental results show the proposed three algorithms have obtained the high security as traditional block-dependent watermarking algorithm and the high localization accurancy as block-independent algorithm by overcoming the disadvantage of low localization accurancy in traditional block-dependent algorithm, which proves the improvement of the proposed two structures in high security and high localization accuracy.A muli-authentication watermarking algorithm has been proposed, and two novel block hierarchy-dividing models have been developed to solve the problem of unselective localization accuracy in traditional image block-dividing watermarking technology. Experimental results show the proposed algorithm can detect and localize the image alters with mutli-levels, and we can choose different localization accuracy with the actual requirements, which highly improves the flexibility and practicality of the image block-dividing algorithms.The imperceptibility of watermarking and the localization of image alter have become the urgen key issues in binary image authentication watermarking technology. Firstly, we have defined a concept of PSD(Pixel spread deviation ) to measure the flippability of the pixels with advantages of little distortion and big capacity. Then, we have proposed a binary image watermarking algorithm based on hierarchical structure. Comparison result with the other algorithms shows the improvement of the proposed algorithm in the watermark imperceptibility and the localization ablility, especially in the protection of uiform regions.A fragile watermark generating model based on chaotic system with high security and generic has been proposed. Considering the general properties of the authentication watermark and the spectrum properties of the chaotic watermark, we have developed the construct principle of the chaotic watermark in image authentication to provide a guide to further research in this area.