Abstract: An adaptive digital watermarking scheme of double keys based on DWT is proposed to protect the copyright of digital image.The digital watermarking scheme extracts the content feature（watermark） from the original image with gradient segmentation threshold 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 characteristic.Due to more and more attacks on it，especially interpretation attack，in this paper，a kind of embedding and recovery method of watermarking is presented after analyzing the principle of attack.It includes double keys from attestation centre and author.This method can solve the interpretation attack and improve the watermarking security.The experiment results show that the embedded digital watermarking by the scheme is invisible and robust enough to watermarking attack，such as JPEG compression，noise，image cropping and median filter.

摘要： 为了更好地保护数字图像的版权，提出了一种基于小波变换域的双密钥自适应水印算法。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；然后利用载体图像的邻域特征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。针对不断出现的各种各样的水印攻击，尤其是解释攻击，通过对其原理的分析，提出了由认证中心分密钥和作者分密钥组成的双密钥水印方案，较好地解决了在抗解释攻击方面存在的问题，提高了水印信息的安全性。仿真实验表明，该自适应水印算法不仅具有良好的不可见性，而且对JPEG压缩、高斯噪声、图像剪切和中值滤波等攻击具有理想的鲁棒性。