Resilience evaluation of digital watermarking methods based on orthogonal transforms

In this paper, we present a comparative study on robustness of digital watermarking methods for copyright protection that are based on orthogonal transforms. The orthogonal transforms are Discrete Cosine Transform (DCT) and Discrete Wavelet Transform (DWT). In experiments, we embed a watermark in the frequency domain of a still image using DCT or DWT. Then we evaluate the degradation in image quality due to the insertion of a watermark. Also, we evaluate the robustness of the watermark against various attacks (scale, index color, gradation conversion, and frequency conversion) with the evaluation support system JEWELS. Experimental results are summarized in regard to the PSNR value of each attacked image and the corresponding extraction level of the watermark.