CAPTCHA
From Computing and Software Wiki
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| - | A CAPTCHA can be described as ''poor'' in one of two ways. Either the test fails to be human-solvable in a reasonable amount of time, or it can be solved by a computer using current AI techniques. | + | ===Poorly Made CAPTCHA=== |
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| + | A CAPTCHA can be described as ''poor'' in one of two ways. Either the test fails to be human-solvable in a reasonable amount of time, or it can be solved by a computer using current AI techniques. | ||
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| + | To the right are two CAPTCHA that fall under the first category. The first image displays a CAPTCHA that requires the user to solve a difficult calculus problem in order to proceed. While this may successfully thwart a bot, it also prevents many legitimate users from using the web service. Likewise, the second example CAPTCHA is simple unreadable by humans due to poor contrast. | ||
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| + | [[Image:Aicaptcha.jpg|left|thumb|300px|A CAPTCHA that has been successfully solved by a computer]] | ||
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===Accessibility=== | ===Accessibility=== | ||
Revision as of 17:01, 7 April 2009
CAPTCHA is an acronym for Completely Automated Public Turing Test to Tell Computers and Humans Apart. Commonly, these tests take the form of images of scrambled text that a human is able to read, but current optical character recognition software cannot decipher. The most common use of a CAPTCHA is to protect web-accessible services from being abused by "bots".
Contents |
Background
Weaknesses
Poorly Made CAPTCHA
A CAPTCHA can be described as poor in one of two ways. Either the test fails to be human-solvable in a reasonable amount of time, or it can be solved by a computer using current AI techniques.
To the right are two CAPTCHA that fall under the first category. The first image displays a CAPTCHA that requires the user to solve a difficult calculus problem in order to proceed. While this may successfully thwart a bot, it also prevents many legitimate users from using the web service. Likewise, the second example CAPTCHA is simple unreadable by humans due to poor contrast.
Accessibility
References
- Carnegie Mellon University. 2009. What is a CAPTCHA?.
- Chesnut, Casey. 2005. Using AI to beat CAPTCHA and post comment spam
- Luis von Ahn, Ben Maurer, Colin McMillen, David Abraham and Manuel Blum. 2008. reCAPTCHA: Human-Based Character Recognition via Web Security Measures. In Science.
- Luis von Ahn, Manuel Blum, Nicholas Hopper, and John Langford. CAPTCHA: Using Hard AI Problems for Security. In Eurocrypt.
- Luis von Ahn, Manuel Blum and John Langford. 2004. Telling Humans and Computers Apart Automatically. In Communications of the ACM.
- W3C. 2005. Inaccessibility of CAPTCHA.
- Willis, John M. 2008. Top 10 Worst Captchas.
