CAPTCHA

• Computers: Internet: Abuse  (114)
• Computers: Internet: Abuse: Comment Spam  (22)
• Computers: Internet: E-mail: Spam: Preventing  (68)

Captcha Creator :

- PHP Captcha Script that generates unique captcha images to stop automated submissions, highly customizable, easy to install and configure.
CAPTCHA: Telling Humans and Computers Apart Automatically :

- Includes demonstrations, research papers, and news.
Inaccessibility of CAPTCHA :

- A W3C Working Group Note explaining how CAPTCHAs can present a major obstacle to users who have limited vision or a learning disability such as dyslexia. This document examines a number of potential solutions and alternative systems.
JCaptcha :

- An open source Java framework for captcha definition and site integration. Project information, documentation, issue tracker, and download.
reCAPTCHA :

- A captcha system that uses successful decodings to helps digitise books for online use. Background, and details on how to incorporate into a site. Source code in several languages, and plugins for popular blogging and CMS software.
RNIB Web Access Centre Blog: CAPTCHA - If Your Name's Not Down You're Not Coming In :

- Article outlining the accessibility issues with CAPTCHAs, and describing some possible solutions, none of which are found by the authors to be completely satisfactory.
Securimage :

- Open source PHP script for generating image CAPTCHAs with audio alternatives. Includes documentation, a gallery and an online demonstration. [LGPL]
Wikipedia: CAPTCHA :

- Explains how captcha features can keep spammers from signing up for certain accounts online, such as email or weblogs. Explains how the system can be circumvented as well.