利用DCT方法，嵌入水印。可设置像素修改值、选择各种经典的攻击方式和控制攻击强弱。返回提取的水印信息和峰值信噪比。利用Matlab编写。-The use of DCT approach, embedding the watermark. Modify pixel values can be set to choose a variety of classic attacks and control the strength of the attack. Back to extract the w