Lazyweb, let me ask a more specific photo booth-related question:

Let's say you have two devices, a Mac Mini and a black box that has a cash-input slot and a credit card reader.

1. What is the make and model of that black box?
2. How does software running on that Mac have the dialog:
   "Dear user, give me two dollars now" →
   "Oh, I see that you have, hooray."

I have done a bit of searching on said black boxes, and there are many of them, but I can't determine what the interface to any of them is, whether it's "pin goes +5v" or what. Something less caveman than that would be nice, obviously.

Previously.