说明：  基于DWT的水印算法 对图像进行二层小波分解，提取出二层低频系数，随机选取一些像素，根据选定像素与其邻居的关系，确定水印的值 水印是根据图像来获得的，而不是提前得到的 根据论文 An Improved Robust Watermarking Technique in Wavelet Domain 编写
(Based DWT watermark algorithm Layer wavelet decomposition, the image is extracted Layer low frequency coefficients, and randomly select some of the pixels, According to the relationship between the pixel and its neighbors is selected, it is determined the value of the watermark of the watermark is based on the image obtained, rather than in advance by According to the papers ' An Improved Robust Watermarking Technique in Wavelet the Domain' writing)