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In this dissertation, the methods of protection and authentication for digital images are presented. In the study of fragile image authentication, the method that can thwart the counterfeit attack is proposed in Chapter 2, and we analyze this method in order to prove the effect. In the study of semi-fragile image authentication, two image authentication methods with digital signature-based and digital watermark-based are presented in Chapter 3 and Chapter 4 respectively. These two methods can improve the disadvantages of related works, and the main contributions are: (1) can adjust the fragile degree by assigning the least authenticable bound of image and (2) the related theorems about the proposed methods are analyzed completely. Finally, a new issue and solution about semi-fragile image authentication are presented in Chapter 5. The main contributions of this method are: (1) only the spatial domain is adopted during feature generation and verification, making domain transformation process is unnecessary, (2) more reasonable non-malicious manipulated images (JPEG, JPEG2000 compressed and scaled images) than related studies can be authenticated, achieving a good trade-off of image authentication between fragile and robust under practical image processing, and (3) non-malicious manipulation is clearly defined to meet closely the requirements of sending them over the Internet or storing images.

ABSTRACT ROBUST DATA HIDING SCHEME WITH TURBO CODES &Uuml / NAL, BariS M.S., Department of Electrical And Electronics Engineering Supervisor: Prof. Dr. R&uuml / yal ERG&Uuml / L December 2005, 127 pages This study describes the design and implementation of a robust data hiding algorithm which is provided by turbo codes. As the digital technology grows up, it is getting easy to copy and distribute multimedia products without getting legal permission. This has forced researchers to study in digital watermarking areas. Along with watermarking researches, data hiding studies have gained interest in the last decade. Different watermark and data hiding algorithms have been proposed considering different requirements and properties such as robustness, fidelity, invisibility and data hiding capacity. In this thesis, robustness of watermarking systems and fidelity requirement in watermark models are considered and use of turbo codes is proposed with data embedding systems to improve system performance in terms of robustness. Fundamental watermarking algorithms in DCT domain are analyzed and simulated. Their performances in terms of robustness are presented. Data hiding algorithm which is based on projection and perturbation in transform domain is implemented in visual C. Then turbo codes are applied to this algorithm to improve system robustness. Improvement provided by turbo codes is demonstrated and compared with other discussed watermarking systems.

The ease of digital media modification and dissemination necessitates content protection beyond encryption. Information hidden as digital watermarks in multimedia enables protection mechanism in decrypted contents. The aims of this research are three-fold: (i) to investigate the strength and limitations of current watermarking schemes, (ii) to design and develop new schemes to overcome the limitations, and (iii) to evaluate the new schemes using application scenarios of copyright protection, tamper detection and authentication. We focus on geometrically robust watermarking and semi-fragile watermarking for digital images. Additionally, hybrid schemes that combine the strength of both robust and semi-fragile watermarks are studied. Robust watermarks are well suited for copyright protection because they stay intact with the image under various manipulations. We investigated two major approaches of robust watermarking. In the synchronization approach, we employed motion estimation for watermark resynchronization. We also developed a novel watermark resynchronization method that has low computational cost using scale normalization and flowline curvature. In another approach, we firstly analyzed and improved a blind watermark detection method. The new method reduces significantly the computational cost of its watermark embedding. Secondly, we created a geometric invariant domain using a combination of transforms, and adapted the blind watermark detection method that we improved. It totally eliminates the need of resynchronization in watermark detection, which is a very desirable achievement that can hardly be found in existing schemes. On the other hand, semi-fragile watermarks are good at content authentication because they can differentiate minor image enhancements from major manipulations. New capabilities of semi-fragile watermarks are identified. Then, we developed a semi-fragile watermarking method in wavelet domain that offers content authentication and tamper localization. Unlike others, our scheme overcomes a major challenge called cropping attack and provides approximate content recovery without resorting to an original image. Hybrid schemes combine robust and semi-fragile watermarks to offer deductive information in digital media forensics. We firstly carried out a pilot study by combining robust and fragile watermarks. Then, we performed a comparative analysis on two implementation methods of a hybrid watermarking scheme. The first method has the robust watermark and the fragile watermark overlapped while the second method uses non-overlapping robust and fragile watermarks. Based on the results of the comparative analysis, we merge our geometric invariant domain with our semi-fragile watermark to produce a hybrid scheme. This hybrid scheme fulfilled the copyright protection, tamper detection, and content authentication objectives when evaluated in an investigation scenario.