一种新的自适应半脆弱水印算法

A Novel Adaptive Semi-fragile Watermarking Scheme Based on Image Content

提出了一种基于图像内容的自适应半脆弱数字水印算法．该算法首先结合梯度分割阈值选取策略,自适应抽取图像内容特征并作为水印信息;然后利用载体图像邻域特性自适应确定量化步长,并通过量化调制小波系数嵌入数字水印;最后通过比对提取出的水印信息与重新抽取出的图像内容特征,实现对待检测图像的完整性检验和篡改定位．仿真实验证明,该自适应半脆弱图像水印算法不仅具有较好的篡改检测与定位能力,而且具有较强的抗攻击能力．

This paper proposes a novel semi-fragile watermarking scheme, which is robust against regular manipulations, for image authentication. The semi-fragile watermarking scheme extracts the content feature （watermark） from the original image by adaptively gradient partitioning, and inserts this content feature back into the image by modulating the wavelet coefficients. To enhance the robustness and invisibility of this scheme, the adaptive quantization step is calculated according to the local image characteristics. The integrity authentication and tamper detection are implemented by comparing the extracted watermark and the extracted content feature. Experimental result shows that if there is no change in the obtained image, the watermark will be correctly extracted, and thus will pass through the authentication system. This scheme is tolerant of regular manipulations （such as JPEG2000 compression）, but malicious changes of the image will result in breaches of the watermark detection. In addition, this scheme can detect the exact locations-the illegal modified blocks.