A Watermarking Scheme Based on the Characteristic of Addition among DCT Coefficients

Generally, low frequency domain may be useful to embed a watermark in an image. However, if a watermark is embedded into low frequency components, blocking effects may occur in the image. Then considering blocking effects, we study some characteristics among DCT coefficients and find some interesting mutual relations. Here, the robustness of many schemes based on the orthogonal transformations such as DCT may be doubtful against geometric transformations. For the distortions produced by some geometric transformations, we propose a searching protocol to find the watermarked block which is rotated and shifted. In the proposed scheme, a watermark can remain in the attacked image with very high probability in our scheme. Further, the watermark becomes more robust than the above scheme using error-correction.