Semi Fragile Watermarking Based on Wavelet Transform
Watermarking schemes are traditionally classified into two classes, robust watermarking and fragile watermarking. Recently a third type of watermarking called semi fragile watermarking has been proposed. Using semi fragile watermarking a user can determine whether the image is tampered with or not for individual applications. For this purpose semi fragile watermarking should indicate the degree of tampering correctly. Most semi fragile watermarking schemes can indicate the position of tampering for localized alteration. Most of them, however, cannot indicate the degree correctly for lossy compression such as JPEG, since lossy compression changes almost all pixels’ values. In this paper we will propose a new semi fragile watermarking technique based on the wavelet transform. The proposed scheme embeds multi-valued watermarks to wavelet coefficients for evaluating the degree of tampering for each pixel. It is proven that the proposed scheme can evaluate the degree of JPEG correctly for a wide range of SN ratios.
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