> Are there systems that can't be abused through automation, or where that's much less of a concern? Let's analyze. One place CAPTCHA has been used a lot is in

> Are there systems that can't be abused through automation, or where that's much less of a concern? Let's analyze. One place CAPTCHA has been used a lot is in comment forms. It increases the opportunity cost of posting a comment via automation by introducing a complicated challenge. Fair enough. But that doesn't solve the underlying problem (abusive comments). You'll still have abuse and spam, it will just come from humans instead of robots. If I'm a blackhat SEO with a budget, I pay people to solve CAPTCHAs all day and spam the internet (that's what happens). If you design the comment system to fight abuse from the ground up (e.g., markov chain spam filters, user flagging), you don't need to care anymore wether it's a human or a robot behind the POST, because all the spam actually improves your training set. You defeat spammers with their own data.