Answering that question would give potential counterfeiters information on how they can defeat such protocols, right? +5

An ATM (Automatic Teller Machine) DOESN'T know counterfeit from real. Or anything from real, for that matter. One can make a deposit into an account using an ATM and slide an empty envelope into the machine. It will still credit that account with whatever amount you entered on the keypad. HOWEVER, funds deposited into an account by ATM are NOT credited until the next business day, when the contents of the machine are emptied and verified by humans. And if you deposited money into an account by check, the bank's policy concerning the amount of the check and how long it takes to clear are in effect as well. So if they have a 6 day wait policy on checks, the funds deposited by check won't become available until 5 business days AFTER the first business day after the deposit. Now, machines which take bills (like soda machines, change machines, etc.) work differently. They scan the bills which are entered to see what denomination they are and if they are real. The ink used to make real bills is magnetic, and the machine "reads" the bill just like it would an audio cassette: with a "tape head". http://www.ehow.com/how-does_4968111_change-machines-work.html#

I don't know +4