为了更好进行版权保护，提出一种基于关系的DCT域盲提取数字水印算法。首先，对原始图像进行8×8分块的离散余弦变换，根据变换后每一块内的直流系数和中频系数的关系得到一个极性矩阵，将该极性矩阵与最佳置乱处理后的二值水印图像进行对比，根据对比的结果对载体图像的中频系数进行修改达到水印嵌入的目的。在水印的提取过程中不需要原始图像，实现了水印的盲提取。大量的仿真实验结果表明了该算法的有效性。

A blind watermarking algorithm based on the relationship of coefficients in the Discrete Cosine Transform (DCT) domain is proposed. Firstly, the original image is divided into non-overlapping 8×8-pixels blocks, and each block is independently transformed to frequency domain through 2D-DCT. Secondly, according to the relationship of DC and middle-frequency coefficients, a polarity matrix is obtained; and then compare the polarity matrix with binary watermark image after scrambling. Finally, the middle-frequency coefficients of the original image are modified in terms of the comparation result to get thewatermarked image. The binarywatermark is extracted from the watermarked image without the original image. The experimental results show that the algorithm is invisible and robust against the general image processing methods.