How do automated payment machines work?

These automated payments essentially work like any retail store that offers credit card purchases, except the purchase total is determined by a computer instead of a person.

Take a vending machine. You select item "C3". The computer is configured to know that C3 costs $2. When you swipe your card, the machine sends your card information to a card processing vendor. The vendor will then use the card type (Visa, Mastercard, etc.) to determine the account from which to deduct the $2. The card processing vendor subtracts any fees (usually 1% - 5%), and then sends the rest to the owner of the vending machine.

You cannot just connect a computer and interface with the payment hardware specifically. You might be able to hack the vending machine to change the cost of C3 to $0. But all the communication between the hardware and the processing vendor would be encrypted.

There are basically 2 methods:

1. Either say parking place installs a terminal unit connected and accepts the card via internal systems just like any shop would do - than the rules of this unit and the general rules are subject in first row to the agreement they have with their supplier and than general consumer laws, or
2. This device is run by a bank (or somebody on behalf of the bank) and connected to banking network and than it is ATM = Automatic Teller Machine. Basically a replacement of banking window in some bank. This allows far wider functionality, like dispensing cash, changing your pin, applying for a credit-line and so on.

Card accepters usually run very simple, cheap, small, light 1 function devices while banking devices are far larger and have far more functions. Actually they are full computers that used to run usually OS/2 and you could have different applications loaded and custom developed.