CAPTCHA Resources
"CAPTCHA" is an acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart" and is a test that some use to determine whether the user is human. Tests are based upon the concept that a computer will not be able to respond correctly to certain kinds of questions. If the correct solution is entered, the presumption is that the respondant is human. On this basis, CAPTCHAs may be considered where there is a desire to prevent automated systems from gaining access to specific web services such as using contact/comment forms or forum posts.
Whilst CAPTCHAs can be effective in limiting abuse by automated systems, they also pose significant accessibility barriers for some user groups. The following resources have been suggested by Guild members as recommended reading for anyone who is considering implementing a CAPTCHA:
- CAPTCHAs on Social Networking Sites Shut Out Blind Users
A video presentation illustrating the problems with graphical CAPTCHAs (Requires Macromedia Flash) - Inaccessibility of CAPTCHA: Alternatives to Visual Turing Tests on the Web
A Word Wide Web Consortium (W3C) Working Group document produced by the Web Accessibility Initiative (WAI) Protocols and Formats Working Group - CAPTCHA: TheFAQs
Why CAPTCHAs are Gotchas for some users - Matt Presents: Escape from CAPTCHA
Suggestions for alternatives to CAPTCHA - Podcast #40: About CAPTCHA and Accessibility
A discussion on different methods of implementing CAPTCHA on the web and how to make it accessible. - How to Use Free Captchas.net and Stop SPAM
Information on a free service that provides web accessible CAPTCHAs - Pretend We're Not a Turing Computer but a Human Antagonist ( PWNtcha)
An interesting project whose goal is to demonstrate the inefficiency of many visual CAPTCHA implementations by breaking them.