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Computer-assisted Instruction (CAI) plays very important role in e-learning system. Distancelearning students can remotely access this kind of course material. As CAI materials are in electronic form they are subject to illegal manipulation and duplication. Therefore, there is growing need to develop robust techniques for protecting these materials. Digital watermarking has been proposed as a solution to the problem of copyright protection of multimedia for many decades. This technique can also be applied to the educational materials. In this paper, a protection scheme is proposed in which double watermarks are embedded into all still images in the CAI materials before they are distributed. Firstly, the visible watermark, e.g., university’s logo, is inserted directly on image pixel’s intensity to exhibit an ownership. An invisible, semi-fragile watermark is then also embedded on these watermarked images. Because of the special characteristic of the latter watermark, any attempt to change or remove the visible logo can be clearly detected. We have also developed an extraction method to reveal the secret watermarks which verify our right on the CAI materials. We have conducted experiments using different kinds of attacks on the watermarked images. The results of these experiments are discussed and conclusions presented as to the reliability and applicability of our proposed scheme.

Security in CAI Materials by Embedding Digital Watermarks