A new fragile watermarking scheme, which exploits the perturbation in reverse processing, is proposed to enhance the tampering localizability of multimedia authentication. In verifying data integrity or authenticating signatures, the new method performs the reverse processing of watermark embedding. Typically, it solves an embedding equation or de-filters the distributed version instead of really extracting the watermark. If any tampering happened, the output of the method perturbs because the manipulated data, which can be regarded as the observation error, is drastically enlarged by such processing. The perturbed values indicate the degree of the tampering, and their positions directly draw the shapes of the manipulated areas. Compared with the mostly used block-based fragile watermarking, the new method localizes the tampering almost sample-wise other than block-wise. It also supports the adaptive embedding, which does not evenly scale the watermark, and avoids the vulnerabilities resulting from the block-based approaches.
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