Extension:ReCAPTCHA

What can this extension do?
reCAPTCHA places a strong CAPTCHA on your wiki. The CAPTCHA helps to read books that are scanned by projects such as archive.org. The CAPTCHA also includes an accessible audio version. Researchers at Carnegie Mellon University believe that this CAPTCHA is not readable by current OCR technology.

Usage
See http://recaptcha.net/plugins/mediawiki/ for instructions.