A CAPTCHA is a program that protects websites against bots by generating and grading tests that humans can pass but current computer programs cannot. For example, humans can read distorted text as the one shown below, but current computer programs can't:
The term CAPTCHA (for Completely Automated Public Turing Test To Tell Computers and Humans Apart) was coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas Hopper and John Langford of Carnegie Mellon University.
Get a Free CAPTCHA For Your SiteA free, secure and accessible CAPTCHA implementation is available from the reCAPTCHA project. Easy to install plugins and controls are available for WordPress, MediaWiki, PHP, ASP.NET, Perl, Python, Java, and many other environments. reCAPTCHA also comes with an audio test to ensure that blind users can freely navigate your site. reCAPTCHA is our officially recommended CAPTCHA implementation.
reCAPTCHA helps prevent automated abuse of your site (such as comment spam or bogus registrations) by using a CAPTCHA to ensure that only humans perform certain actions.
It's Free! Yep, reCAPTCHA is free.
It's Useful. Why waste the effort of your users? reCAPTCHA helps to digitize books.
It's Accessible. reCAPTCHA has an audio test that allows blind people to freely navigate your site.
It's Secure. Most other CAPTCHA implementations can be easily broken.
It's Popular. Over 100,000 sites use reCAPTCHA, including household names like Facebook, Ticketmaster, and Craigslist.
It's Easy. reCAPTCHA is a Web service. As such, adopting it is as simple as adding a few lines of code on your site. For many applications and programming languages such as Wordpress and PHP we also have easy-to-install plugins available. We generate and check the distorted images, so you don't need to run costly image generation programs.
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