Athanasios Nikolaidis

Asymptotically optimal detection for additive watermarking in the DCT and DWT domains

Most of the watermarking schemes that have been proposed until now employ a correlation detector (matched filter). The current paper proposes a new detector scheme that can be applied in the case of additive watermarking in the DCT (discrete cosine transform) or DWT (discrete wavelet transform) domain. Certain properties of the probability density function of the coefficients in these domains are exploited. Thus, an asymptotically optimal detector is constructed based on well known results of the detection theory. Experimental results prove the superiority of the proposed detector over the correlation detector.

Region-based image watermarking

We introduce a novel method for embedding and detecting a chaotic watermark in the digital spatial image domain, based on segmenting the image and locating regions that are robust to several image manipulations. The robustness of the method is confirmed by experimental results that display the immunity of the embedded watermark to several kinds of attacks, such as compression, filtering, scaling, cropping, and rotation.

Facial feature extraction and pose determination

Abstract A combined approach for facial feature extraction and determination of gaze direction is proposed that employs some improved variations of the adaptive Hough transform for curve detection, minima analysis of feature candidates, template matching for inner facial feature localization, active contour models for inner face contour detection and projective geometry properties for accurate pose determination. The aim is to provide a sufficient set of features for further use in a face recognition or face tracking system.

A benchmarking protocol for watermarking methods

A benchmarking system for watermarking algorithms is described. The proposed benchmarking system can be used to evaluate the performance of watermarking methods used for copyright protection, authentication, fingerprinting, etc. Although the system described is used for image watermarking, the general framework can be used, by introducing a different set of attacks, for benchmarking of video and audio data.

Robust watermarking of facial images based on salient geometric pattern matching

We introduce a novel method for embedding and detecting a chaotic watermark in the digital spatial domain of color facial images, based on localizing salient facial features. These features define a certain area on which the watermark is embedded and detected. An assessment of the watermarking robustness is done experimentally, by testing resistance to several attacks, such as compression, filtering, noise addition, scaling, cropping and rotation.

A survey on watermarking application scenarios and related attacks

A thorough investigation on all possible scenarios where digital imperceptible watermarking is applicable is presented. All previously proposed watermarking schemes fall to at least one of the referenced application categories. Possible attacks are divided into categories and application scenarios are presented, always referring to the watermarking parameters involved.

Performance analysis of correlation-based watermarking schemes employing Markov chaotic sequences

In this paper, theoretical performance analysis of watermarking schemes based on correlation detection is undertaken, leading to a number of important observations on the watermarking system detection performance. Statistical properties of watermark sequences generated by piecewise-linear Markov maps are investigated. Correlation/spectral properties of such sequences are easily controllable, which is a fact that reflects on the watermarking system performance. A family of chaotic maps, namely the skew tent map family, is used to verify the theoretical analysis. Skew tent chaotic sequences are compared against the widely used pseudorandom sequences, indicating the superiority of the former in watermarking applications. The minimum number of samples required for reliable watermark detection is also investigated. Experiments using audio data are conducted to verify the theoretical analysis results.

Applications of chaotic signal processing techniques to multimedia watermarking

Usage of digital media has witnessed a tremendous growth during the last decades. However digital media are extremely vulnerable to copyright infringement, tampering and unauthorized distribution. Recently the protection of digital information has received significant attention within the digital media community and a number of techniques that try to address the problem by hiding appropriate information within digital media have been proposed. In this paper we present two applications of chaotic systems to watermarking of multimedia data, namely secure spatial scrambling of watermark patterns prior to their embedding in images and generation of 1-D or 2-D watermark signals.

Comparison of different chaotic maps with application to image watermarking

The current paper presents a method for image watermarking based on chaotic sequences produced by different functions. The effect of embedding a chaotic watermark on an image is examined. Extensive experimental results for JPEG and filtering attacks on images watermarked by the different functions are presented together with a comparative study of them. The results show that efficient watermarking methods based on chaos can be designed under certain conditions.

Statistical analysis of a watermarking system based on Bernoulli chaotic sequences

The paper deals with the statistical analysis of the behaviour of a blind copyright protection watermarking system based on chaotic watermark signals generated by n-way Bernoulli shift maps. The analysis involves theoretical evaluation of the system detection reliability, when a correlator detector is used. The effect of distortions (lowpass filtering, noise corruption of the watermarked data) on the detection reliability is also theoretically investigated. The system is modelled in a communication framework considering the signal as interference and converting the addressed problem to the detection of the underlying watermark signal. The aim of the paper is two-fold: (i) to introduce the n-way Bernoulli shift generated chaotic watermarks and theoretically contemplate their properties with respect to the detection reliability and (ii) to theoretically establish their potential superiority against the widely used (pseudo-)random watermarks. An important property of Bernoulli watermarks is their controllable spectral/correlation properties that renders them ideal for a variety of applications. Bernoulli watermarks can be generated with lowpass spectral properties to withstand lowpass attacks. When no distortions are to be inflicted, white spectrum Bernoulli watermarks can be generated so that their performance converges to that of the random watermarks. Experimental verification of the theoretical analysis results has been performed as well.