ScatterType: a legible but hard-to-segment CAPTCHA

The ScatterType CAPTCHA (completely automated public Turing tests to tell computers and humans apart), designed to resist character-segmentation attacks and shown to be highly legible to human readers, is analyzed for vulnerabilities and is offered for experiments in automatic attack. As introduced in Baird and Riopka (2005), ´ScatterType´ challenges are images of machine-print text whose characters are cut into pieces which then drift apart, in an attempt to frustrate segment-then-recognize computer vision attacks. Analysis of experimental human legibility data has shown that better than 95% correct legibility can be achieved through judicious choice of the pseudorandom generating parameters (Baird et al., 2005). That analysis is summarized and discussed here as motivation for a discussion of potential vulnerabilities. An invitation to attack ScatterType is offered.