现有的基于分块的无损图像认证算法难以确定合适的认证块大小．为此，文中提出了一种认证块大小可动态调整的无损图像认证算法．该算法的图像认证块分别由若干基本图像块组合而成，相应的认证信息用数字签名技术产生，以无损水印方式嵌入，同时通过多次无损嵌入方式实现图像编号的鲁棒传送，用图像编号区分不同图像、防止矢量量化攻击．理论分析与实验结果表明，该算法可有效抵抗矢量量化攻击，图像认证块的大小能根据宿主图像特征和水印图像保真度要求进行动态调整，有效地提高了篡改定位能力．

As the existing block-wise lossless image authentication algorithms cannot determine appropriate sizes of image authentication blocks,a novel lossless image authentication algorithm with size-variable authentication blocks is proposed. In this algorithm,an image authentication block is composed of some basic image blocks,and the authentication code is generated by using a digital signature algorithm and is embedded into the authentication block via the lossless watermarking. Moreover,the robust transmission of the image ID is achieved via multiple embedding,which helps to distinguish different images and to resist the vector quantization attack. Theoretical analyses and experimental results demonstrate that the proposed algorithm can not only effectively resist the vector quantization attack but also improve the tamper localization accuracy because it can dynamically adjust the sizes of authentication blocks according to the characteristics of the host image and the fidelity threshold of the watermarked image.