A two-level novel reversible image authentication scheme based on chaotic fragile watermark is proposed to locate tampered pixel accurately and ensure security of image. In the embedding process,at the pixel level,by utilizing the pixel correlation technology,the location watermark of each pixel is generated and embedded to the LSB of the pixel itself. At the image block level,the image is then par-titioned into blocks,then the relation and detection watermark of each block is computed and embedded into the top-left sub-block of its corresponding excursion block and the down-right sub-block of the block itself in a reversible way respectively. In the extracting process,the watermarked image is partitioned into blocks,the embedded detection and relation watermark of each block is extracted and the block is recovered,then computing the new relation watermark and detection watermarks of each recovered block and performing comparison with the extracted ones. In the proposed scheme,the tampered watermark can pass the authentication because it does not re-duce the value of image to some extent. But if the image content is tampered,the further step is taken at the pixel level to locate tamper to specific pixel by comparing the re-computed location watermark with the extracted location watermark. Theoretical analysis and com-puter simulation also indicates that the algorithm is feasible and efficient,especially in multimedia application requiring both integrity and confidentiality of the original image.%针对多媒体数字图像易遭攻击的安全性问题，文中提出了一种基于混沌脆弱水印的可逆双层图像认证方案。在发送端，首先通过像素关联技术产生像素级的定位水印，并将其嵌入到自身的LSB位。然后把图像分成大小相同的块，先后计算每块的关系水印和检测水印，并分别用可逆的方法嵌入到偏移块的左上角和自身块的右下角。在接收端，首先对图像进行分块；然后通过比较提取和重新计算的水印来确定是否有篡改发生，并可以区分是内容篡改还是水印篡改。当内容被篡改时，可通过定位水印将篡改进一步定位到具体的像素，否则可以通过认证。大量的理论分析和实验仿真结果表明，该算法具有可行性和高效性，在同时需要认证和完整恢复原始图像的多媒体应用中表现得尤为明显。
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