A Contour-Based Semi-fragile Image Watermarking Algorithm in DWT Domain

To authenticate image content tolerant to lossy compression, a semi-fragile image watermarking algorithm based on contour is proposed in this paper. The Y subdivision of original image is subdivided to 4×4 blocks and executed 2-level DWT transform first, then filtered contour image derived from Canny edge detector is used as image feature to generate a watermark. Arnold transform is performed on watermark image to destroy space relativity. Watermark embedding is realized through changing the relationship of selected middle DWT coefficients according corresponding watermark bit. The subtraction result of calculated contour image and extracted watermark image is used to authenticate the content of the image. There is no perceptible degradation to original image. Experiments show that the scheme is useful to meet the requirements of image content authentication and no acceptable JPEG compression is rejected.