I suspect there is no theoretically perfect solution to CAPTCHA. Bot must get good at emulating user and software must get better at identified users. None of o

I suspect there is no theoretically perfect solution to CAPTCHA. Bot must get good at emulating user and software must get better at identified users. None of our interaction with computer are non-emulatable so the war would be indefinitely ongoing. But what we can do is to make it expensive for bot to emulate user. One way to do this is creating ID system which requires some form of payment and thus creating an ID and expensive proposition. For example, Amazon can make their user account as open ID for logins and provide the target system a flag IsVerifiedPurchaser. Payments don't have be strickly in direct monetary forms also. For example, Facebook can estimate ad revenue generated by an user so far and provide some flag as to whether user is active and trustable as not being a bot.