View Printable Version

Abdelkader H. Ouda, Fall 2004, "Digital Watermarking Techniques for Image Security and Hidden Communication", Computer Science Department, University of Western Ontario, Canada.

Ph.D. Thesis Abstract

Popular media (television, movies, magazines, etc.) has frequently tried to present information in the form of images. The question is then raised, "Are we going to authenticate the images that we have just seen?". The answer could come down to the level of trust in the photographer and media outlet. However, in our present globalization era, this generally is not achievable. Thus, unless we have image authentication techniques, such images will be difficult to verify.

Suppose that you have posted a rare (valuable and/or unique) photograph on your website. If this photo appears in another medium, such as a famous magazine, where the credit and money go to someone else, are you able to prove your ownership for this photo? Unless you have used image copyright protection techniques to encode your copyright information on your digital photograph before putting it on your website, you cannot.

In addition, one can encode secret information in the image allowing the secret information to be sent in an environment where encryption is not permitted. This might be done using "Hidden Communications" techniques. These techniques could allow the exchange of secret messages without attracting much attention. The main contribution of this dissertation is the development of three promising digital watermarking techniques, which enable image authentication, copyright protection, and hidden Communication.These techniques are designed using two kinds of technologies, namely cryptography and steganography. Cryptography can be defined as a science of secret writing, whereas steganography is the art and science of communicating in a way, which hides the existence of the communication.

An image dependent hashing function is proposed, which utilizes correlation coefficients statistics to measure the image pixels relationships. This function produces an image dependent hash value that is quite short when compared with those produced by other cryptographic hashing functions. Also, a new watermark embedding approach is introduced, where the cryptosystem is used to embed the watermark rather than encrypt the watermark itself. This approach helps increases the localization accuracy for most existing block-based watermarking techniques. Hence, a novel image watermarking technique for image authentication has been implemented. This technique is able to provide greater assurance that the image has not been modified. However, if modifications occur, the location of these modifications will be accurately identified.

An enhancement to the general steganography model has been made. This enhancement adopts a cryptographic shared key mechanism, where a new key generation module is introduced. It generates a shared secret key between parties based on their public information. This enhancement affects the vast majority of watermarking techniques, either for copyright protection or hidden communication.

Moreover, a new approach for information hiding is introduced. This approach is compatible with the JPEG2000 image compression standard. The information will be embedded during the rate/distortion optimization phase. While the capacity of the hidden information is inversely proportional to compression level, the hidden information is robust against the JPEG2000 compression ratios. Finally, an image copyright protection technique that utilizes this approach is proposed.

Keywords: digital watermarking, steganography, cryptography, information hiding, image authentication, copyright protection, and hidden communication.