Captcha system used by wikipedia ?

Best alternative to reCAPTCHA

[Future]

I have observed thousands of captcha systems acrross number of sites, some being unique like recaptcha acquired by google recently, (worst part for small sites).

What system is used by wikipedia, they seem to be very easy to follow by novice users ?

[bill]

I think it's the same one included in MediaWiki.

[Future]

bill,
Thank You for your reply, we spend almost a week figuring the right answer, but cannot rely if your answer is right ?

We found wikipedia captcha, as the best and simple solution for all our readers, but cannot understand the same..

I hope, if you can shred some light if you can hint us *(via mediawiki atleast I was not able to get answer)

Thank You again.

[bill]

Wikipedia is run on MediaWiki. Compare the CAPTCHA on a default install of MediaWiki to the CAPTCHA you're talking about and you'll have your answer.