说明：  数字水印的常见几种攻击方法，已经写成函数，高斯噪声、椒盐噪声、乘性噪声、中值滤波、维纳滤波、JPEG压缩、剪切攻击、旋转攻击、行列偏移攻击等
(Several common attack methods of digital watermarking have been written as functions, such as Gaussian noise, salt and pepper noise, multiplicative noise, median filter, Wiener filter, JPEG compression, clipping attack, rotation attack, row column offset attack, etc)