> It seems more likely they are trying to steal cc details by asking for such a small payment.
This relates to being afraid using a credit card online against a non credible seller.
> Payment processing is nontrivial to set up
This one is about the technical difficulty (And possibly also regulation) for setting up payment processing
> regions where it is uncommon to have means to interface with payment processors.
This one is about inaccessibility to payment means, which also relates to a problem with the payment medium.
I assume that bo1024 suggested this because he implicitly believes that setting up a payment processor will be more difficult, and give bad experience to the user.
The only objection I have seen which is more specific to actually recognizing humans is this one (by Freak_NL)
> What would prevent the bots from using the same system?
First, I think that it should make operating bots on a wide scale much more expensive. Second, if you make money out of bots coming into your website, would you really care that they are bots? I assume that the reason someone would block bots from the first place is that bots harm their money making business. If you had a system to collect this money back, shouldn't this considered as a problem solved?
I am working these days on a decentralized payment system that supports micro-payments. (I promise there are no blockchains inside). Solving the captcha thing can be a very useful use case. I will be happy if anyone wants to join forces on this one (My email is real (at) freedomlayer (dot) org).