Most countries heavily restrict the reproduction of images of paper currency, In the USA for instance it is illegal to use digital imagery of paper currency unless it is presented in Black & White only. Actual physical artwork or reproduction of paper currency is only allowed if, again, it is in black and white and is either less than 70% of the original size or greater than 150%. Even the Federal Reserve website has to comply with these rules. All of these rules do not, of course, apply to coinage.