This paper presents a secure (tamper-resistant) algorithm for watermarking images, and a methodology for digital watermarking that may be generalized to audio, video, and multimedia data. We advocate that a watermark should be constructed as an independent and identically distributed (i.i.d.) Gaussian random vector that is imperceptibly inserted in a spread-spectrum-like fashion into the perceptually most significant spectral components of the data. We argue that insertion of a watermark under this regime makes the watermark robust to signal processing operations (such as lossy compression, filtering, digital-analog and analog-digital conversion, requantization, etc.), and common geometric transformations (such as cropping, scaling, translation, and rotation) provided that the original image is available and that it can be succesfully registered against the transformed watermarked image. In these cases, the watermark detector unambiguously identifies the owner. Further, the use of Gaussian noise, ensures strong resilience to multiple-document, or collusional, attacks. Experimental results are provided to support these claims, along with an exposition of pending open problems.

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Computer-assisted Instruction (CAI) plays very important role in e-learning system. Distance- learning 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.

Abstract—In this paper, we present a robust and secure algorithm for watermarking, the watermark is first transformed into the frequency domain using the discrete wavelet transform (DWT). Then the entire DWT coefficient except the LL (Band) discarded, these coefficients are permuted and encrypted by specific mixing. The encrypted coefficients are inserted into the most significant spectral components of the stego-image using a chaotic system. This technique makes our watermark non-vulnerable to the attack (like compression, and geometric distortion) of an active intruder, or due to noise in the transmission link. Keywords—Blind source separation (BSS), Chaotic system, Watermarking, DWT. I.