Hi, artist here. I want to use the moment of attention to ask around for ideas on how to conceptually build the reverse of this. The current idea would be to also use a web wallet, ie. you would preload an easywallet.org wallet with some coins, then give the URL to the machine (type, QR, whatever) and it spits out cash. There must be something more clever to solve the problem of transaction verification (inside easywallet it's instant and we don't have to wait 10m) and authentication (if the machine would receive your bitcoins on a special address, how the machine know you sent it?).