基于邻域比较的JPEG脆弱水印算法及性能分析

摘要

To improve the tamper detection performance and harmonize the conflict between security and invisibility, this paper proposes a fragile watermarking algorithm for JPEG images, in which the authenticity of image blocks is determined by neighborhood comparison. This scheme divides the original image into 8×8 image blocks. For each block, four bits watermarks are generated based on the DCT coefficients to be protected. Next, the watermarks are randomly embedded in the least significant bit (LSB) of DCT coefficients with smaller quantization step in other four blocks. The authenticity of each block is determined by comparison between the number of inconsistent image blocks in the eight-neighborhood of each block and its four corresponding mapping blocks. Then, this paper derives the probability of false acceptance and false rejection under general tampering and collage attack and validates the theoretical analysis results by statistical experiments. Theoretical analysis and statistical experiments show that comparing the number of inconsistent image blocks in the eight-neighborhood of each block with its four corresponding mapping blocks improves the tamper detection performance. Embedding watermarks in the LSB of DCT coefficients with less quantization step efficiently solves the conflict between the number of DCT coefficients to be protected and invisibility.%为提高篡改检测性能和协调安全性与不可见性之间的矛盾,提出一种利用邻域比较判定图像块真实性的JPEG脆弱水印算法.该算法将原始图像分成8×8的图像块,基于图像块保护DCT系数生成的4比特水印基于密钥随机嵌入到其他4个图像块量化步长较小的DCT系数最低位.通过比较该图像块与相应4个水印嵌入块8邻域中不一致图像块个数来判定该图像块的真实性,推导给出一般篡改和拼贴攻击下算法的虚/漏警率,并利用统计实验对理论分析结果进行验证.理论分析和实验统计结果表明,通过比较图像块与其相应水印嵌入块8邻域中不一致图像块个数能够提高篡改检测性能,在量化步长较小DCT系数的最低位嵌入水印,解决了保护DCT系数个数与不可见性之间的矛盾.