利用LSB算法去实现了电子水印技术。代码完全实现了嵌入以及提取， 算法同时包含了4种攻击算法以及利用psnr测量提取的水印和攻击后提取的水印,This algorithm describes digital watermark technique by using LSB. This code implement embedding and extraction. At the meanwhile, this algorithm includes 4 different kinds of attacks and in the end, measure psnr between extracted watermark and attacked extracted watermark