Update [Oct 25, 2010]: NuCaptcha has just launched its advertising offering (here's a promo video).
If you liked ads in CAPTCHAs brought to the world by Solve Media (formerly AdCopy), you'll love NUcaptcha, a company that has developed technology to replace the usual squiggles with animations and videos and that is apparently working on an advertising solution.
Recent (Oct 6) updates to the company's downloadable files talk about how "NuCaptcha can push ads right into a Captcha field, providing a new, highly visible ad space." The description for the WordPress plugin describes NUCaptcha as "a multi purpose product which provides industry leading security combined with brand messaging, advertising and unique user engagement." The image above with the WestJet spec shows up when you browse to the site on an iPad as a replacement for the default Flash sequence.
I'm curious about the patent side of the story. Last March, I wrote about a company in Germany trying to patent video CAPTCHA ads. Microsoft, too, had submitted an application for a patent that describes a CAPTCHA ad system similar to Solve Media's where users type in ad slogans. One of the examples of Solve Media's ads are for Internet Explorer 8; Microsoft's application is illustrated with an ad for Xbox.
Even though CAPTCHA advertising has been a recurring topic on AdLab since 2005, I'm not sure I'm convinced it's a good idea as it may create strong incentives for publishers to opt against the optimum user experience, similar to breaking up articles into multiple pages and slideshows to ramp up page views.
On a related note, I would love to see a reCaptcha-like system used as a foreign language instruction tool, where you are given a word in one language and are asked for a translation in another.