system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a vending machine recognize a dollar as opposed to a dollar sized piece of paper?

I want free snacks and drinks.
gpt
They take a picture.   Your piece of paper doesn't look like a dollar bill.

They read the fine patterns.   Your piece of paper that you tried to commit counterfeitting does have the fine patterns that a real dollar bill has, because your printer isn't capable of printing the fine lines.    Take a magnifying glass to right side of 5 dollar bill, you'll see "five dollars" repeated in the side bar.   You'll see "USA five" on the purple 5.    You'll see names on top of the Lincoln memorial.