If you have ever attempted a life as a counterfeiter, or done a stupid school project where you tried to print your own money, you already know this: you can’t make a copy of any type of bill, no matter the denomination. For older bills, it was because of the Eurion constellation, which is an order of dots that appears on pretty much every major currency. Today, there’s a new counterfeit deterrence system which includes the Eurion constellation but also has other mysterious forces at work.
Source: io9 – Here’s the Reason Why You Can’t Photocopy Money