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Thomas Dowling <[log in to unmask]> wrote: > Does anyone know anything concrete about "cognitive" captchas? I've run > into anecdotal support for things like: > Enter the word "orange" <input name="foo"> [...] > Are these known to work? Or are they just clever guesses about what > bots might not be able to figure out? There are mostly anecdotes because this stuff is hard to test properly. I found they worked a little, but are just clever guesses. "3.1 Logic puzzles The goal of visual verification is to separate human from machine. One reasonable way to do this is to test for logic. Simple mathematical word puzzles, trivia, and the like may raise the bar for robots, at least to the point where using them is more attractive elsewhere. Problems: Users with cognitive disabilities may still have trouble. Answers may need to be handled flexibly, if they require free-form text. A system would have to maintain a vast number of questions, or shift them around programmatically, in order to keep spiders from capturing them all. This approach is also subject to defeat by human operators." Source: http://www.w3.org/TR/turingtest/#logic As that last phrase hints, bots are not the only problem. See http://www.schneier.com/blog/archives/2007/11/spammers_using.html for example. Hope that helps, -- MJ Ray (slef) Webmaster for hire, statistician and online shop builder for a small worker cooperative http://www.ttllp.co.uk/ http://mjr.towers.org.uk/ (Notice http://mjr.towers.org.uk/email.html) tel:+44-844-4437-237