A CAPTCHA is a type of test used to protects website services against use by automated programs that might abuse or otherwise take advantage of the service. The idea is to have a simple question that is easy for a human to answer, but difficult for a computer program. The standard technique is to ask users to type in text shown in an image. Typical applications include protecting registration and comment forms.
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Users need to roll dice and answer the question to verify they are human with this free image based service. Provides a demo, FAQs and customization options.
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.
An open source Java framework for captcha definition and site integration. Project information, documentation, issue tracker, and download.
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.
Open source PHP script for generating image CAPTCHAs with audio alternatives. Includes documentation, a gallery and an online demonstration. [LGPL]
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.
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