Well, if it is solving CAPTCHA better and faster than humans, that is a useful signal. Maybe they monitor how often an IP address figures something out and if i

Well, if it is solving CAPTCHA better and faster than humans, that is a useful signal. Maybe they monitor how often an IP address figures something out and if it gets too many right they +1 a suspicion counter. I dunno. Implementing the CAPTCHA solving bot also takes time and expertise; it'd filter out some low-ability spammers.