Graeme Bell

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This paper discusses and demonstrates the interplay between system security and user interface convenience in CAPTCHA design, and in particular, mobile device CAPTCHA design. A CAPTCHA is a computer-based security test used to distinguish human users from artificial users, preventing automated abuse of networked resources. As mobile network services(More)
—Defeating a CAPTCHA test requires two procedures: segmentation and recognition. Recent research shows that the problem of segmentation is much harder than recognition. In this paper, a new projection-based segmentation algorithm is proposed for the MSN and Yahoo CAPTCHAs. Experimental results show that the proposed algorithm can improve correct(More)
—A fully automated, blind, media-type agnostic approach to ste-ganalysis is presented here. Steganography may sometimes be exposed by detecting automatically characterized regularities in output media caused by weak implementations of steganography algorithms. Fast and accurate detection of steganography is demonstrated experimentally here across a range of(More)
This article highlights legal, ethical and scientific problems arising from the use of large experimental datasets gathered from the Internet-in particular, image datasets. Such datasets are currently used within research into topics such as information forensics and image-processing. This paper strongly recommends against webcrawling as a means for(More)
The advantages of Least-Significant-Bit (LSB) steganographic data embedding are that it is simple to understand, easy to implement, and it results in stego-images that contain hidden data yet appear to be of high visual fidelity. However, it can be shown that under certain conditions, LSB embedding is not secure at all. The fatal drawback of LSB embedding(More)
A CAPTCHA is a test designed to distinguish computer programs from human beings, in order to prevent the abuse of networked resources. Academic research into CAPTCHAs includes designing friendly and secure CAPTCHA systems and defeating existing CAPTCHA systems. Traditionally, defeating a CAPTCHA test requires two procedures: segmentation and recognition.(More)
Simple, universally applicable strategies can help any captcha-protected system resist automated attacks and can improve the ability of administrators to detect attacks. The strategies discussed here cause an exponential increase in the difficulty faced by automated attackers, while only increasing the inconvenience for human users in an approximately(More)
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