Jung-San Lee, Hsiao-Shan Wong and Yi-Hua Wang, Feng Chia University, Taiwan

Most watermark methods use pixel values or coefficients as the judgment condition to embed or extract a watermark image. The variation of these values may lead to the inaccurate condition such that an incorrect judgment has been laid out. To avoid this problem, we design a stable judgment mechanism, in which the outcome will not be seriously influenced by the variation. The principle of judgment depends on the scale relationship of two pixels. From the observation of common signal processing operations, we can find that the pixel value of processed image usually keeps stable unless an image has been manipulated by cropping attack or halftone transformation. This can greatly help reduce the modification strength from image processing operations. Experiment results show that the proposed method can resist various attacks and keep the image quality friendly.

Image watermarking, Discrete Cosine Transform (DCT), variation-free, coordinate system