It occurs to me that the machines that accept dollar bills, to make change or sell you something, must somewhere inside them have something they compare the bill to: a template, stored data that the input from a scanner is compared to, etc. In other words, something that tells the machine “THIS is the definition of what a dollar bill looks like”.
I wonder if any enterprising crooks have tried hijacking a vending machine, tearing it open and reverse-engineering from the template, in order to forge bills that will fool a vending machine, even if they wouldn’t pass a naked-eye inspection for a second.
I dunno about forging a bill, but I once did better on a dollar bill change machine than the slots at Vegas. I put in a buck, it gave me back 5. Another buck, it gave me back 15. By the time I ran out of singles ( I was young and that is all my wallet contained at the time.) I made something like $100 out of a $20 investment. Problem was it was all in quarters so I had to buy rounds that night at the bar ( I was on vacation) paying in change.
A bill-changer could be fooled rather easily, if you had a good color photocopy of a $1 bill. I don’t suggest trying this, however, unless you want the Secret Service to show up at your home.
A few years ago when I was still of the age of doing stupid things and amazingly not getting caught, some friends and I discovered a change machine in one of the campus snack bars would let loose quarters if you rocked it back and forth to an angle of about 50 degrees. We came away with around $70 in quarters that night. No idea if they all do that or if it’s just a quirk of that machine.
That would depend on if its a new or an older one. Almost all of the newer ones also check the ink to see that it conducts electricity, which a photo copier will not do.
When a certain close friend of mine was young and stupid, he would take advantage of this with a 2 liter bottle full of salt-water.
A strip of tape attached to the bill in order to pull it back out once its accepted was the other method that my close friend used.
My close friend has since repented and wouldn’t dream of doing this these days. He thinks he has more then paid back the vending machine companies with all the money he spends now on the way overpriced beverages.