Photocopiers don't let you photocopy money. Modern scanning and printing computer tools don't work with money either. How do they know it's money you're scanning? It's the EURion constellation, a magic pattern of five dots that says "do not copy me". Details in Markus Kuhn's analysis and these images.
It's like a talisman, a symbol with mystical powers that is feared but not understood. The fear is built into copiers and scanners. Adobe went along too so you can't work with currency images in Photoshop, although the feature it detects is not EURion.