Scanners with banknotes remind me of my kid's LeapFrog book. It's basically a book and a pen which can read whatever you tap against. It has an optical sensor a

Scanners with banknotes remind me of my kid's LeapFrog book. It's basically a book and a pen which can read whatever you tap against. It has an optical sensor at the tip of the pen and the print just has a bunch of microscopic dots barely visible to the naked eye. https://en.wikipedia.org/wiki/LeapFrog_Tag https://en.wikipedia.org/wiki/LeapFrog_Tag