提出了一个以8位灰度图像作为水印的DCT域水印算法。首先对以往的基于人眼视觉掩蔽特性(HVS)的块分类方法进行了改进，使其能更充分地挖掘载体图像的信息隐藏能力。在图像水印的嵌入方法上，将水印图像进行DCT变换，然后将DCT系数的低频分量嵌入到拉伸因子较大的块中。同时，对水印图像的DCT系数进行调整，使得各频率的能量基本相当，间接地提高了提取的水印图像的信噪比。实验结果表明，所提出的水印算法对多种攻击具有较好的稳健性，尤其对JPEG压缩、旋转和剪切攻击。其稳健性更明显。

A DCT-domain watermarking algorithm with 8 bits gray image's watermark is proposed. First, the method of block classification based on HVS is improved, which enhances the information hiding ability of cover image. In the watermark embedding process, we transform the image's watermark into DCT domain, and embed the low-frequency coefficients to the blocks that have bigger elongation factor. At the same time, we adjust the DCT coefficients of image's watermark to make them in the same level. This increases the SNR of extracted watermark. The experimental results show that the mentioned algorithm is more robust to many attacks, especially to JPEG compression, rotation and cropping.