You might also be interested in https://github.com/kallerosenbaum/poppoc/wiki/Proof-of-Payment https://github.com/kallerosenbaum/poppoc/wiki/Proof-of-Payme...,

You might also be interested in https://github.com/kallerosenbaum/poppoc/wiki/Proof-of-Payment https://github.com/kallerosenbaum/poppoc/wiki/Proof-of-Payme..., which will let you "login" by prooving that you made a small bitcoin transaction. The disadvantage of this sort of microtransaction is that people may actually be willing to pay more through donation then through forced payment.