Abstract: A semi-fragile image watermarking technique that accepts JPEG lossy compression was developed.With the high sensitivity on initial value of chaotic mapping and the invariant properties of DCT coefficients before and after JPEG compressions,the pre-quantified low DCT coefficients and a watermarking key are combined as the initial value of logistic maps for generating the watermark.The watermarked image was obtained by modifying the DCT coefficients according to the watermark.The number of the image blocks are mapped into the iteration times of chaotic system to resist the counterfeiting attacks on block-wise independent watermarking shemes.Experimental results showed the proposed technique was robust against JPEG lossy compression,but sensitive to the malicious attacks on the watermarked image.At meantime,it can localize the tampers correctly and accurately.

摘要： 提出了一种抗JPEG有损压缩的半脆弱图像数字水印算法。该算法充分利用混沌映射对初值的敏感性,并根据JPEG图像压缩过程中DCT系数的不变特性,将预先量化的DCT低频系数和水印密钥合成为混沌系统的初值,经过多次混沌迭代生成水印。根据水印调整DCT中频系数的大小,完成水印的嵌入调制。通过将图像块的编号映射为混沌系统的迭代次数,避免了针对块独立水印算法的诸如矢量量化等攻击。实验结果表明,该算法对JPEG有损压缩具有良好的鲁棒性,同时可对图像内容的恶意篡改进行精确的检测与定位。