Refining-Localization-Based Image Authentication And Recovery Scheme Using Iterative Compensation Mechanism

The rapid development of multimedia technology and powerful processing tools bring new problems to information security, which cannot be resolved by traditional encryption. Illegal alteration and tampering will cause harm to society and people, so how to protect the integrity of multimedia content is becoming an urgent issue. The technology of digital watermarking, which can overcome the limitation of traditional authentication methods, gives a promising solution to this problem, and becomes a hot research topic. The integrity and authenticity of digital images belong to multimedia information security.The dissertation proposes a refining localization watermarking for image tamper detection and recovery. To enhance the accuracy of tamper localization, the algorithm contains basic authentication and refining authentication. Basic authentication can locate all blocks that contain the tampered pixels by the basic authentication watermark. Refining authentication can exclude some genuine pixels from the tampered blocks by the refining authentication watermark. The algorithm fuses the two authentication results and optimizes the fusion result by the number of pixels in connected tampered regions to obtain the accuracy authentication result. The recovery watermark, which is generated using the important DCT coefficients, is embedded into the mapping block. According to the authentication result, if the mapping block of a block that contains tampered pixels is authentic, the algorithm can use the information that is embedded into the mapping block to recover the tampered pixels; otherwise, the algorithm cannot recover the tampered pixels. The simulation results show that the proposed algorithm can improve the accuracy of tamper localization and can approximately recover the tampered pixels.In the refining localization watermarking scheme, because of the disadvantages of the block-mapping technology, we use iterative compensation mechanism to recover the tampered pixels in the second research work. Recovery watermark is constructed by applying matrix operation on the five most significant bit-planes of all pixels by two different keys, and is embedded into the entire image dispersedly. The process of image authentication and tamper localization is the same as the process in the refining localization watermarking scheme, but the process of recovery uses iterative compensation mechanism to recover the tampered pixels. Experimental results show that the proposed scheme improves the probability of recovering the tampered pixels.