Watermarking techniques are primarily used for copyright protection. In this paper, a simple and robust watermark-like digital authentication scheme is proposed. This work has two major merits. First, the watermark used in the proposed authentication scheme is the same type used in the original image, e.g., grey level images. Second, the proposed scheme meets the requirements for watermarking techniques. Illegal users cannot perceive and break the watermark signed from the original image. Furthermore, the signed watermark is robust against attacks by many image altering algorithms, such as filtering, lossy compression, rotation, and scaling. The proposed scheme is not only suitable for ordinary natural images, but also for cartoon graphics.

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Recently, Wu and Chieu proposed a user-friendly remote authentication scheme with smart card. In their scheme, the users can choose and change their passwords freely. However, their scheme is insecure. In this paper, we propose two attacks on their scheme.

Watermarking techniques are primarily used for copyright protection. In this paper, we propose a digital watermarking scheme, which is based on neural network, cryptography, and image processing techniques. Our scheme can achieve the following two goals. The first is that illegal users do not know the location of an embedded watermark in the image. The second is that a legal user can retrieve the embedded watermark from an altered (filtering, lossy compression, and scaling) image. The security and robustness of the proposed scheme are improved using neural network technology.

CAPTCHA has been widely used for preventing malicious programs to access web resources automatically. In this paper, a new type CAPTCHA system will be proposed. The proposed scheme, named Clickspell, combined the features of text-based and image-based CAPTCHAs. Clickspell asks users to spell a randomly chosen word by clicking distorted letters for passing the test. Users can learn the definition(s) of the chosen word. In addition, Clickspell can add an advertisement image optionally. Thanks to the advertisement image, Clickspell improved the capability of resistance to the attack by malicious programs. Our preliminary test showed that Clickspell is practical in the aspects of security and usability.