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Much research in recent years has focused on the introduction of virtual learning environments (VLEs) to universities, documenting practice, and

Digital Watermarking is an ever increasing and important discipline, especially in the modern electronically-driven world. Watermarking aims to embed a piece of information into digital documents which their owner can use to prove that the document is theirs, at a later stage. In this paper, performance analysis of watermarking schemes is performed on white noise sequences and chaotic sequences for the purpose of watermark generation. Pseudorandom sequences are compared with chaotic sequences generated from the chaotic skew tent map. In particular, analysis is performed on highpass signals generated from both these watermark generation schemes, along with analysis on lowpass watermarks and white noise watermarks. This analysis focuses on the watermarked images after they have been subjected to common image distortion attacks. It is shown that signals generated from highpass chaotic signals have superior performance than highpass noise signals, in the presence of such attacks. It is also shown that watermarks generated from lowpass chaotic signals have superior performance over the other signal types analysed.

In this paper we investigate the limits on optical detection of noisy watermarks that use a chaotic function, the logistic difference equation, in the watermark generation scheme. By varying the function seed, different chaotic sequences exhibiting lowpass and highpass characteristics, can be obtained for the same function, offering an added security advantage over watermarks generated using pseudorandom sequences. Watermark Detection is the process of determining whether an image is watermarked with a certain watermark. In this paper, we model and investigate an optical correlator suitable for watermark detection for certain classes of high-pass or low-pass watermarks. Once in the public domain a watermarked image may be subjected to noise and other attacks, deliberate and unintentional. Additionally, an optical correlator system will also be subject to shot noise. The effects of shot noise on optically transmitted watermarks are modeled in this paper and we examine how the watermark detection scheme performs in such situations. We quantify the degree of noise that may be present in the watermark detection scheme in order to obtain reliable detection or rejection of a watermark using an optical-correlator.

A digital watermark is a visible, or preferably invisible, identification code that is permanently embedded in digital media, to prove owner authentication and provide protection for documents. Given the interest in watermark generation using chaotic functions a detailed study of one chaotic function for this purpose is performed. In this paper, we present an approach for the generation of watermarks using the logistic map. Using this function, in conjunction with seed management, it is possible to generate chaotic sequences that may be used to create highpass or lowpass digital watermarks. In this paper we provide a detailed study on the generation of optically detectable watermarks and we provide some guidelines on successful chaotic watermark generation using the logistic map, and show using a recently published scheme, how care must be taken in the selection of the function seed.