提出了一种基于匹配滤波的有意义水印盲提取算法，通过构造基于特征子空间的正交水印信号集，水印的提取不需要原始图象，而且误码率可以控制在较低的水平，基于特征子空间分解特性，具有简单有效的特点，同时由于水印信号集由原始图象唯一生成，并具有一定的不可逆性，因此可以防止水印攻击者利用非法产生的水印集来伪造有意义的水印。实验结果证明了该算法具有较好的稳健性和不可见性，为了对提取字符的可靠性进行评价，还提出了一种置信度门限，利用置信度门限可以有效地评估单个字符及整体水印的可靠性，弥补了一些算法只提取有意义水印，而不加评估的缺点。

In this paper, a blind meaningful watermarking algorithm is proposed. The host image is first transformed into wavelet domain where the feature set is extracted. Through subspace decomposition of the feature set, the watermark signal sets are generated which holds orthogonality between each two watermark signals and between the watermark signals and the feature set. For the orthogonality between the watermark signals and the feature set, the meaningful watermark can be extracted without resorting to the host image. And for the orthogonality between each two watermark signals, the characters embedded can be retrieved robustly using matched filtering. Because the watermark signal sets are image content dependent, the algorithm security can be improved. In order to measure the reliability of the extracted characters, the concept of credibility threshold is proposed by which the wrong characters can be correctly pointed out. Therefore the credibility of the whole message can also be evaluated, which is another contribution of this paper. In the experiment, we test the algorithm performance under JPEG compression and Additive White Gaussian Noise(AWGN). The results show that the robustness and imperceptibility of the watermark are satisfactory. The credibility threshold also proves its effectiveness.