掌握基本数字水印和DCT数字水印的实现和检测方法；检验DCT数字水印，抵抗高斯噪声攻击、椒盐噪声攻击、剪切攻击和旋转攻击的能力。(Grasp the implementation and detection methods of basic digital watermarking and DCT digital watermarking, and test the ability of DCT digital watermarking to resist Gauss noise attack, salt and pepper noise attack, shear attack and rotation attack.)