[munger]

Yeah this.

SEO/internet marketers who want to go create a bunch of spammy backlinks through user profiles / blog comments on forum sites and blogs (anything that allows account creation and user generated content) to target affiliate marketing sites they own have pretty great automated tools to do this that integrate with the commercial captcha solving services.

The captcha solving aspect is around $1 - $1.50 per 1000.

You can't really prevent this and it really doesn't matter how effective the captcha is because outsourcing the human required to solve it is so ridiculously cheap.