A CAPTCHA which humans find to be highly legible and which is designed to resist automatic character-segmentation attacks is described. As first detailed in [BR05], these 'ScatterType' challenges are images of machine-print text whose characters have been pseudorandomly cut into pieces which have then been forced to drift apart. This scattering is designed to repel automatic segmentthen-recognize computer vision attacks. We report results from an analysis of data from a human legibility trial with 57 volunteers that yielded 4275 CAPTCHA challenges and responses. We have located an operating regime-ranges of the parameters that control cutting and scattering-within which human legibility is high (better than 95% correct) even though the degradations due to scattering remain severe.

We present a method for rapid development of benchmarks for Semantic Web knowledge base systems. At the core, we have a synthetic data generation approach for OWL that is scalable and models the real world data. The data-generation algorithm learns from real domain documents and generates benchmark data based on the extracted properties relevant for benchmarking. We believe that this is important because relative performance of systems will vary depending on the structure of the ontology and data used. However, due to the novelty of the Semantic Web, we rarely have sufficient data for benchmarking. Our approach helps overcome the problem of having insufficient real world data for benchmarking and allows us to develop benchmarks for a variety of domains and applications in a very time efficient manner. Based on our method, we have created a new Lehigh BibTeX Benchmark and conducted an experiment on four Semantic Web knowledge base systems. We have verified our hypothesis about the need for representative data by comparing the experimental result to that of our previous Lehigh University Benchmark. The difference in both experiments has demonstrated the influence of ontology and data on the capability and performance of the systems and thus the need of using a representative benchmark for the intended application of the systems.

The ScatterType CAPTCHA, designed

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We propose a forward selection method that constructs