Athanasios Nikolaidis

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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(More)
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,(More)
In this paper 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 in the paper is used for image watermarking, the general framework can be used, by(More)
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(More)
A thorough investigation on all possible scenarios where digital imperceptible watermarking is applicable is presented in this paper. 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(More)
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(More)
The purpose of this article is to present a novel method for region based image watermarking that can tolerate local image distortions to a substantially greater extent than existing methods. The first stage of the method relies on computing a normalized version of the original image using image moments. The next step is to extract a set of feature points(More)
The current paper describes a new technique for embedding secret data in JPEG compressed color digital images. Emphasis is given in improving effective payload percentage over file size increase while retaining low distortion levels. The proposed technique is based on modification of non-zero quantized coefficients. In contrast to previously proposed(More)
The current paper introduces a novel method for inserting data in a grayscale image without the need to include any overhead information in order to pinpoint the embedding positions or any other alteration of gray values. The method is semi-reversible in the sense that the hidden data are correctly extracted, whereas the original image is not necessarily(More)