published_or_final_version / Community Medicine / Master / Master of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

published_or_final_version / Architecture / Master / Master of Philosophy

No description available.

The proliferation of collaborative computer applications in the past decade has resulted in a corresponding increase in the need for multi-user interfaces. The current research seeks to contribute to the design of a user-centered multi-user interface for a group ranking task. User requirements were identified by observing groups perform the ranking task in a non-computer environment. A design was proposed based on these identified requirements. The user-centered design was compared to preliminary designs based on the intuitions of programmers. The conclusions indicate that an analysis of observations in the non-computer environment does yield insight beyond the initial intuition of programmers. A prototype based on the user-centered design was implemented. Informal user evaluation was performed by observing users working with the prototype and obtaining verbal feedback both on the ease of use of the system and on possible improvements. The informal user evaluation provides evidence for the usefulness of user-centered design. The evaluation also suggests that not all features identified were found useful and not all features necessary were identified.

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No description available.

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No description available.

Steganography is classified as the art of hiding information. In a digital context, this refers to our ability to hide secret messages within innocent digital cover data. The digital domain offers many opportunities for possible cover mediums, such as cloud based hiding (saving secret information within the internet and its structure), image based hiding, video and audio based hiding, text based documents as well as the potential of hiding within any set of compressed data. This dissertation focuses on the image based domain and investigates currently available image based steganographic techniques. After a review of the history of the field, and a detailed survey of currently available JPEG based steganographic systems, the thesis focuses on the systems currently considered to be secure and introduces mechanisms that have been developed to detect them. The dissertation presents a newly developed system that is designed to counter act the current weakness in the YASS JPEG based steganographic system. By introducing two new levels of randomization to the embedding process, the proposed system offers security benefits over YASS. The introduction of randomization to the B‐block sizes as well as the E‐block sizes used in the embedding process aids in increasing security and the potential for new, larger E‐block sizes also aids in providing an increased set of candidate coefficients to be used for embedding. The dissertation also introduces a new embedding scheme which focuses on hiding in medium frequency coefficients. By hiding in these medium frequency coefficients, we allow for more aggressive embedding without risking more visual distortion but trade this off with a risk of higher error rates due to compression losses. Finally, the dissertation presents simulation aimed at testing the proposed system performance compared to other JPEG based steganographic systems with similar embedding properties. We show that the new system achieves an embedding capacity of 1.6, which represents round a 7 times improvement over YASS. We also show that the new system, although introducing more bits in error per B‐block, successfully allows for the embedding of up to 2 bits per B‐block more than YASS at a similar error rate per B‐block. We conclude the results by demonstrating the new systems ability to resist detection both through human observation, via a survey, as well as resist computer aided analysis. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2010.