Abstract: A blind watermark algorithm of gray image is proposed based on DCT.At first，the watermark image is scrambled and encrypted.Then the vector image is divided into 8×8 blocks.Each block is transformed by DCT and watermark is embedded by quantization rules for the use of plus or minus.Watermark detection is based on positive and negative quantitative rules，and doesn’t need the original image.It’s a blind detection.At last，evaluating the performance of watermarking algorithm is done through the watermark correlation coefficient（NC） and Peak Signal to Noise Ratio（PSNR）.Experimental results show that the algorithm can effectively resist JPEG compression，noise，shearing，filtering attacks，and has a better robustness.

Key words: digital watermarking, Discrete Cosine Transform（DCT）, quantization of plus or minus, blind detection

摘要： 提出一种基于离散余弦变换（DCT）的灰度图像盲水印算法。首先对水印图像进行置乱加密。然后将载体图像进行8×8大小的分块，针对各分块进行DCT变换，采用正负量化规则进行水印的嵌入。水印的检测是根据正负量化规则进行的，不需要原始图像，是一种盲检测。最后通过水印相关系数（NC）和峰值信噪比（PSNR）来评价水印算法的性能。实验结果表明，该算法可以有效地抵抗JPEG压缩、噪声、剪切、滤波等攻击，鲁棒性较好。

关键词: 数字水印, 离散余弦变换（DCT）, 正负量化, 盲检测