Papers about CAPTCHAS

This is a very short selection of paper about CAPTCHAs. A CAPTCHA (source, Wikipedia) is a test used to prevent bots from submutting Web forms automatically, although they have several other applications. You must have seen one, at least! Want an example? OK, just comment this post :-) Well, take this one by the very CAPTCHA creators:

I have uploaded a number of paper to CiteUlike. It is so easy...

If you want to check them, just click on the link: papers about CAPTCHAs. Or if you prefer to get informed when I upload more, subscribe to the RSS feed :-) (If I were you, I would rather subscribe to my whole library feed).