Fragile watermarking is used to detect the authentication and integrity of digital media. The tamper detection performance and the security of a fragile watermarking scheme are two important evaluation measures. This paper proposes a secure pixel-based fragile watermarking scheme, in which the watermark data of each pixel is generated and embedded based on the secret key. Using the pixel-neighborhood comparison, the tamper detection performance is improved without increasing the watermark payload. In the proposed scheme,the chaos system is used to generate the binary watermark data according to the content of each pixel in the original image. The improved security binary watermark by scramble encryption was embedded into the least significant bit of the image data. In tamper detection process, the validity of the test pixel is determined by comparing the number of the inconsistent pixels in a pixel-neighborhood of it with the predefined threshold.The method of the dynamic threshold selection and the relationship between the tamper ratio and the probabilities of false acceptance and false rejection are discussed. Theoretical analysis and simulation results show that the proposed method can distinguish the modifications on the content from the watermark and resist the collage attack, and detect the tampered pixels with a probability of nearly 1.%脆弱水印用于鉴定数字媒体的真实性和完整性,篡改检测性能和安全性是脆弱水印算法的两个重要指标.本文提出一种基于密钥生成和嵌入像素水印信息的安全脆弱水印算法,在不增加水印嵌入容量的前提下,采用邻域像素比较的篡改检测方法有效提高算法的篡改检测性能.本文首先利用混沌迭代生成水印信息,然后将生成的水印信息置乱加密后嵌入在原始图像的最低位.认证时,通过比较像素邻域中不一致像素数目与设定阈值的关系判定像素的有效性,并推导给出阈值的动态选取方法和篡改比例与虚、漏警概率关系.理论分析和实验结果表明该算法不仅能抵抗拼贴攻击(Collage Attack),而且提高精确定位水印算法的篡改检测性能.
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