中文摘要：

为提高图像的篡改定位和恢复能力，提出一种空域与频域结合的分层自嵌入水印算法。第1层水印嵌入把2X2图像块内元素的奇偶校验码、异或校验码以及图像块的灰度均值信息作为水印进行加密后都嵌入到偏移块中，将处理过的偏移块元素的奇偶认证码嵌入其自身。第2层水印嵌入将嵌入第1层水印的图像分成8×8大小，提取每块频域特征加密后的信息嵌入到偏移块。分3层对图像进行检测定位与恢复，给出基于混沌序列与Torus同构映射结合的偏移值选取方法，以增强密钥安全性。实验结果表明，该算法可以同时抵抗字典搜索攻击、拼贴攻击、盲攻击以及大面积的剪切攻击，能准确地定位图像的篡改位置并且图像的恢复质量较高。

英文摘要：

To improve the ability of image tamper detection and recovery, this paper proposes a layered watermark algorithm based on the combination of the spatial and frequency domain. In layer 1, one part of the watermark information authenticating a single pixel in a block with the size of 2 × 2 pixels is embedded into self-block, and the other part together with recovery watermark are embedded into the mapping block. In layer 2, the image processed in layer 1 is divided into blocks with the size of 8 × 8. The frequency information is extracted and embedded into the mapping block. Three layers are used for image detection and recovering tampered image. This paper also proposes an offset value selection scheme based on chaos sequence and Torus isomorphic mapping to improve the safety of the secret keys. Experimental results demonstrate that the proposed algorithm can not only resist dictionary search attack, collage attack,blind attack and large area cropping attack but also locates the tampered blocks precisely with high quality of the recovered image.