> The problem is coming up with challenges that are not trivial to automate and not annoyingly hard for users. > I think trying to come up with challenges to b

> The problem is coming up with challenges that are not trivial to automate and not annoyingly hard for users. > I think trying to come up with challenges to beat botters would be prohibitively time consuming. I agree that is challenging, and I think this question will need to be settled empirically. Sub-questions include: a) What is the threshold for bot operators to engineer custom CAPTCHA solutions? (e.g. for a large website, how much can a bot network make?) b) Even if it were not possible to conclusively beat the bots, what is the threshold at which bot operators decide that they would rather make their money off of other sites instead?