H. Lim, M.E. Lee, S.Y. Park, S.J. Kang, and W.H. Cho (Korea)
Security, Copyright protection, Watermarking, Digital im age
In this paper, we present a robust watermarking technique for secure copyright protection of digital images. The proposed technique employs a block operator which is scanned on DCT coefficients in the zig-zag ordering in the AC subband. To achieve a good balance between imperceptibility and robustness to compression and signal processing techniques, « curve which controls the strength of watermark while embedding watermark in the form of a spread spectrum sequence, is estimated adaptively to the local statistics of DCT coefficients in a moving block. After embedding one of watermark sequence into every coefficient in the block, the detection algorithm uses an adaptive trimmed mean in the block as a local estimate of the embedded watermark to obtain the desired robustness in the presence of attacks. The performance is analyzed through statistical analysis and numerical experiments. It is shown that the robustness properties against additive noise, JPEG compression and signal processing modifications are more enhanced than the previous techniques.
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