Classification of watermarking schemes robust against loss of synchronization

The resistance of watermarking schemes against geometrical distortions has been the subject of quite much research in the last ten years. The ability for a communication scheme to cope with a loss of synchronization is indeed a very difficult issue. Still, the tolerance of the human visual perception in presence of such distortions is surprisingly high and situations where loss of synchronization takes place are numerous. The aim of this paper is to present an extensive survey of existing works addressing this particular problem. Each of the proposed class of techniques are analyzed to show which forms and what severity of distortions it is able to survive. The possible security implications of the proposed techniques is also be studied. We try to point out the strengths and weaknesses of each solution. Special attention is given to implementation details such as cropping operation which is subsequent to most geometrical distortions. Partial loss of content, change of width to height ratio or modification of the image size have important consequence on some proposed schemes. We also briefly discussed the difficulty to evaluate the severity of a geometrical distortion.Anglai