Sharif Digital Repository

Widespread transfer of digital files over networks provides a hidden channel to transfer secret messages. Current steganalysis schemes need to work on a complete image for doing the detection job that starts when the image is entirely transferred, so are often restricted to an offline process. This restriction is serious when existence of the hidden message carriers on the network is shorter than the time required for the detection process. In this thesis, we propose a structurally fast detection method to detect the data hidden in an image passing through network. We use two of most powerful steganalysis algorithms for steganalysis of images that proposed by 1) Fridrich and Pevny and 2) Liu... 

Image steganalysis is the technique and art of detecting covert communication via images.Reduction of features dimentionality is an important issue according to accuracy and time complexity. In this thesis, GA (genetic algorithm) and PSO (Particle Swarm Optimization) are used to reduce the dimentionality of JRM, a recently proposed feature set containing 11255 features which looks high dimentional compared to other feature sets which has been reduced by evolutionary algorithms so far. So, inspite of other works done using evolutionary algorithms in this field, we use the class sepearability criterion as fitness function instead of the accuracy of the classifier. Investigating these features,... 

A major goal in image steganography is to preserve the statistical properties of the host image to thwart statistical based steganalysis. However, most steganography methods introduce some distortions into the host signal’s statistical properties that have been used, as a certain indication of manipulation of the signal, by steganalysis algorithms. In order to overcome such a methodical vulnerability, a new generation of data hiding algorithms has been proposed in the literature to preserve histogram of the host signal. In this thesis we present a novel image steganographic technique to preserve one-dimensional and two-dimensional histograms of the host image. Experimental results show that... 

The advent of digital age with the Internet revolution has made it extremely convenient for users to access, create, process, copy, or exchange multimedia data. This has created an urgent need for protecting intellectual property in both the digital and the print media. Digital watermarking is a suitable way to do this. In this technology, some hidden information called watermark are embedded into host signal and extracted to confirm copyright protection. However, the watermark should be embedded in the host in such a way that the attacks could not destroy it. Print and scan is a popular attack that is applied on digital images. This attack has complex nature and can be implemented easily.... 

Up to now, compared with the comprehensive research for developing robust watermarking algorithms, no equal attention has been devoted to the proposition of benchmarks tailored to assess the watermark robustness. In addition, almost all the state of the art benchmarks only integrate a number of common image processing operations like geometrical transformations to remove watermarks. However, the quality of the processed image is often too degraded to permit further commercial exploitation. Moreover, to the best of our knowledge, the design of these tools does not take into account the statistical properties of the images and watermarks in the design of attacks. In spite of the significant... 

LSB embedding in spatial domain with very low rate can be easily performed and its detection in spite of many researches is very hard, while BOSS competition has been held to break an adaptive embedding algorithm with low rate. Thus, proposing powerful steganalyzer of very low rate in spatial domain is highly requested. In this thesis it has been tried to present some algorithms to detect secret message with very low rate in spatial domain using eigenvalues analysis and relative auto-correlation of image.First approach is based on the analysis of the eigenvalues of the cover correlation matrix that we used for the first time. Image partitioning, correlation function computation,... 

The field of digital image processing refers to processing digital images by means of a digital computer. One of the principal applications used in digital image processing is image compression. Image compression is the problem of reducing the amount of data required to represent a digital image. The basis of the reduction process is the removal of redundant data. One of the other principal applications of image processing is noise reduction (filtering) of images corrupted with additive noise. Filtering techniques are oriented toward modeling the degradation and applying the inverse process in order to recover the original image. Image watermarking is another application of image processing.... 

The advent of Internet and advancement of computer technologies have enabled convenient and fast exchange of multimedia so the illegal reproduction and modification of digital media has become increasingly serious. Hence, how to protect the intellectual property rights of digital multimedia is an imperative issue. Digital watermarking is one of the solutions to prevent unauthorized use of images. Traditional digital watermarking techniques embed a watermark such as logo, trademark, or copyright information into a host image so that it is not perceptible. These techniques, depending on the amount of embedded data, will distort the content of host image which results in quality degradation of... 

Digital watermarking is an efficacious technique to protect the copyright and ownership of digital information. Traditional image watermarking algorithms embed a logo in the image that could reduce its visual quality. A new approach in watermarking called zero watermarking doesn’t need to embed a logo in the image. In this algorithm we find a feature from the main image and combine it with a logo to obtain a key. This key is securely kept by a trusted authority. In this thesis we show that we can increase the robustness of digital zero watermarking by a new counter detection method in comparison to Canny Edge detection and morphological dilatation that is mostly used by related works....