Integrity Verification Of Digital Image Watermarking Algorithm Self-healing

With the development of internet and multimedia technology, the authentication of digital media becomes more and more important. Powerful publicly available image processing software packages such as Adobe PhotoShop, Microsoft Paint and PaintShop Pro make digital forgery a reality. It is possible to carefully tamper an digital image while leaving barely detectable traces by using these tools. So, the problem is how to ensure the integrity of image content. The purpose of this thesis is to authenticate the integrity of a digital image using watermarking technology, which is to check if the image has been tampered and identify the tampered portions. If possible try to recover portions of the image that have been tampered without accessing the original image.In the past, several techniques and concepts based on data hiding or steganography have been introduced as a means for tamper detection in digital images and for image authentication-fragile watermarks, semi-fragile watermarks, and self-embedding watermarks. The research of this thesis mainly includes self-embedding and semi-fragile watermarks. We propose several watermarking techniques after analyzing other watermarking methods detailedly. The main contributions can be summarized as following:(1) Based on previous work, we proposed an improved spatial self-embedding watermarking technique. We save the quantized DCT coefficients using group encoding while not using bit matrix which restricts saving bit length of each DCT coefficient. This method has many advantages compared to the latter and is testified by many images.(2) Because fractal coding has the characteristic of high compression ratio, this thesis designed a spatial self-embedding watermarking technique. After self-embedding, it can detect any changes to a watermarked image as well as localizing the areas that have been tampered. It is also possible to recover portions of the image which have been tampered. Experiments on real images verify the effectiveness of the proposed technique.(3) Since the current self-embedding watermarking techniques are too fragile to resist noise or JPEG compression, we proposed a self-embedding method based on JPEG images which plays an important role in current internet environment.(4) Designed an image authentication method of semi-fragile watermarking technique based on DWT. We transform the image into wavelet domain and group the four adjacent wavelet coefficients. Utilizing the characteristics of the human visual system, we embed a digital signal into the average value of the four adjacent wavelet coefficients since the average value has better stability than single wavelet coefficient. This method needn't original image when the watermark is extracting. Experiment results show the effectiveness of this method which is robust to common image process and fragile to malicious attack, i.e. this method can detect the tampered portions.