I linked to an article about captcha advertising yesterday, so here is some links I’ve collected on the subject. I have found the following four services so far:

AdCopy – In beta, you can request an invite.

AdCaptcher – Advertiser functionality coming soon.

AdAptcha – Also in closed beta, you can request an invite.

CaptchaAd – These guys are open for business. The counter on their site says they have served 23 million captcha ads so far.

The idea of captchavertising (see what I did there, I made a new word) has been popping up every now and then for the past few years.

http://adverlab.blogspot.com/2005/10/captcha-advertising.html

Probably the earliest mention of “captcha advertising”.

http://sethgodin.typepad.com/seths_blog/2006/12/commercializing.html

Next year Seth Godin comes up with it.

http://adverlab.blogspot.com/2007/01/captcha-advertising-part-ii.html
http://www.seobook.com/captcha-advertising

http://adverlab.blogspot.com/2010/03/captcha-advertising-closer-to-reality.html

http://www.techi.com/2010/04/captcha-advertising-coming-soon-to-a-website-near-you/

http://www.captchaadvertising.com/ – One of the above companies should grab this domain.

http://captchavertising.com – Parked.  Seems like I’m not the first one to think of “captchavertising”.

http://captchadvertising.com/ – Also parked.