说明：  对图像进行DCT变换和DCT逆变换，将原始图像和变换后的图像对比，同时将原始水印图像与逆变换后提取的水印图像进行对比
(The image is transformed by DCT transform and DCT inverter, and the original image is compared with the transformed image, and the original watermark image is compared with the watermark image after the inverse transformation.)