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