With rapid growth in computer network and information technology, a large number of copyrighted works now exist digitally as a computer files, and electronic publishing is becoming more popular. These improvements in computer technology increase the problems associated with copyright enforcement and thus future developments of networked multimedia systems are conditioned by the development of efficient methods to protect ownership rights against unauthorized copying and redistribution. Digital watermarking has recently emerged as a candidate to solve this difficult problem. In the first part of this paper we introduces an overview to digital watermarking: The general framework, its main applications, the most important properties, the main aspects used to classify watermarking, and we discuss the attacks that watermarking system may face. Finally we introduce human visual system and its interaction with watermarking as well as some open problems in digital watermarking. In the second part we introduces an overview of watermarking in frequency domain. The general properties for frequency domain as well as specific properties for each sub-domain are introduced. The sub-domains considered are discrete cosine domain, discrete wavelet domain and discrete Fourier domain. We also introduce some different watermarking techniques in each category.

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[41] Zaho J. and Koch E., “Embedding Robust Labels into Images for Copyright Protection,” in Proceedings of the International Conference on Intellectual Property Rights for Information, Knowledge and New Techniques, Munchen, Wien, Oldenbourg Verlag, pp. 242-251, 1995. Khaled Mahmoud received his BSc and MSc degree in computer science from the University of Jordan. Currently, he is a lecturer in the Department of Computer Science at Zarqa Private University, Jordan, and working in his PhD thesis at Loughborough University, UK. His research is in print security and watermarking. Sekharjit Datta received his BSc degree from the University of Calcutta and the MSc and PhD degrees from the University of London. He spent twenty years in industrial research relating to information technology and advanced signal processing, at the Research and Advanced Development Centre of International Computers Ltd, UK, where he worked as a senior research consultant. He became a member of academic staff at Loughborough University in 1987. His research activities have concentrated on various aspects of advanced signal processing. He has specific expertise in the areas of speech, image, bio-acoustic signal processing, and pattern recognition. He has authored/ co-authored over 130 publications in refereed journals and international conference proceedings. James Flint is a lecturer in wireless systems engineering at Loughborough University, UK. He gained a PhD in electronic and electrical engineering for work on efficient electromagnetic modelling of vehicles and was subsequently employed in the Research Department of MIRA Ltd, UK as a project engineer. His current research is in the area of applied signal processing and includes the modelling of novel transducers and the design of high- integrity processors for automotive applications. He is a member of IEEE and IEE, UK, and is a chartered engineer.