为了提高图像认证的可靠性,提出了一种用于图像内容认证的可恢复半脆弱数字水印方案，该方案不仅能鉴别数字图像内容的真实性，还可近似恢复图像中被篡改的区域。该方案基于半色调处理技术，首先将图像半色调处理后生成的二值水印图像经JBIG2压缩后作为嵌入水印，然后经量化索引调制嵌入小波域。用该方案嵌入水印后的图像，在检测时，不但可以定位图像中被篡改的区域，还可以对提取的恢复水印进行解压，并可通过逆半色调处理来重建原图像，用它的对应部分替换被篡改区域来实现对被篡改图像的篡改恢复。此外，由于该算法采用密钥来控制水印的嵌入位置，从而保证了水印的安全性；仿真实验是采用一般性操作和篡改操作相结合的方法，实验结果表明，该算法在保护数字图像内容真实性方面是可行的。

A recoverable semi fragile watermarking algorithm for image content authentication is proposed. The algorithm employs a compressed halftoned binary image as watermark and embeds it in the wavelet domain through quantization index modulation. It can not only detect the tampered area, but also recover it through decompressing and inverse halftoning the watermark image. Beside, a secret key is used to select the embedded watermark bits and their embedded positions to increase the security of watermarking. Experimental results show that this semi fragile watermarking algorithm is effective and practical for content authentication.