CAPTCHAs can be used by MediaWiki wikis to prevent spam. Several implementations currently exist in extensions. Extension:ConfirmEdit is the base framework upon which other CAPTCHA extensions are generally built.
Thay are utilized as a means of ostensibly preventing spam and deterring spammers. In most wikis, a user might hit a CAPTCHA when trying to create an account, create a new page, or add an external link to a page.
Main issues 
There are a number of problems with the current CAPTCHA implementation.
- They are only available in English (bugzilla:5309): the words used by our CAPTCHAs, however they are created, should be in the user's language. An unknown number of new users and edits are lost from non-English speaking people.
- They violate accessibility principles (bugzilla:4845).
- They don't effectively prevent bots from spamming.
Image CAPTCHAs 
Replacing CAPTCHA with a honeypot 
One possibility for avoiding localizations issues with the CAPTCHA is simply to remove it and replace it with a honeypot.
A homegrown reCAPTCHA clone 
Write a version of reCAPTCHA that uses document images that have been processed by MediaWiki's ProofreadPage extension for Wikisource: WikiCAPTCHA. In other words, a CAPTCHA that feeds data to ProofreadPage to augment its OCR processing. You might build on existing code. It is worth noting that "reCAPTCHA hold no specific patents for the technology behind their text CAPTCHA algorithms (At least none they discuss on their website or are able to be found on the US Patents & Trademark Office site)", according to one blogger ().
Filed as bug 32695.
Also discussed at Wikimania 2012 with the presentation Wikicaptcha: a ReCAPTCHA-like solution for Wikisource
See also 
- Admin tools development, the field of Wikimedia Engineering responsible for this and other tools
- Bug 38640
- Research:Account creation UX/CAPTCHA
- TEDxCMU -- Luis von Ahn -- Duolingo: The Next Chapter in Human Computation
- Recent discussions
- Captchas and non-English speakers I and II
- Wikipedia CAPTCHA repair (2011-11-03): «Now that the Wikipedia CAPTCHA has been comprehensively broken by Burzstein et. al. in their paper "Text-based CAPTCHA Strengths and Weaknesses" [...] I've reworked the 2005-era CAPTCHA-image-generating Python script in the CAPTCHA engine» – code still waiting for reviewers.
- Suggestion: replace CAPTCHA with better approaches (July 2012)