ABSTRACT Media authentication and tampering localization are important in content delivery via untrusted intermediaries, such as peer-to-peer (P2P) file sharing. Many differently encoded versions of a media file might exist. Our previous work applied distributed source coding to authenticate the legitimate diversity of encoded images and also localize the tampered regions in an inauthentic image. The authentication/localization decoder was supplied with a Slepian-Wolf encoded image projection as authentication data. We extend our scheme to localize tampering in contrast and brightness adjusted images using an Expectation Maximization algorithm at the decoder. Experimental results demonstrate that tampered image blocks can be identified with high probability using data of only a few hundred bytes for a 512x512 image.

Now a days, the rate of using digital image is increasing exponentially because of its low cost and easy manipulation property. It is obvious that digital images captured from CCD cameras or other digital image devices have to be analyzed and determined before processing it, to keep the integrity and ensure the accuracy and reliability of the digital image. We need some sort of robust methods and standard procedures that guarantee and strengthen the authenticity of digital image. Image authentication is a technique that analyzes a digital image and determines whether it is altered or not. Image authentication technique is very useful for various organizations such as health care, law enforcement agencies and insurance sector etc. Image authentication is also important in content delivery via untrusted intermediaries, such as peer-to-peer (P2P) file sharing. Untrusted intermediaries might tamper the contents of image. Distinguishing the legitimate diversity of encodings from malicious manipulation is the challenge addressed in this paper. We developed a LDPC and watermark based new approach for image authentication. With the help of this approach we can authenticate images effectively. In our technique, we provide LDPC quantized image projection and the Encrypted image as authentication data. As well as watermark image that was embedded into original image to identify legitimate or illegitimate state of image authentication system. These data can be correctly decoded only with the help of an authentic image as side information. This technique provides the desired robustness against legitimate encoding alteration, while detecting illegitimate variations.

In the 1970’s Slepian and Wolf proved that lossless source coding without side information at the encoder may perform as well as encoding with side information at the encoder. Wyner and Ziv extended the result to establish ratedistortion bounds for lossy compression. This has been used to examine the problem of coding multiple correlated distributed sources. In distributed coding, source statistics are exploited at the decoder and the encoder can be simplified. Since then these theoretic results were revisited in the late 1990s and several methods have been developed to achieve the results predicted by the theory. They are generally based on the channel coding techniques. In the past several years we have seen a great deal of work done in distributed video coding.