As far as I know many countries use Digimarc for their money.

EDIT: Here is a source:

    Recent versions of image editors such as Adobe 
    Photoshop or Paint Shop Pro refuse to print banknotes. 
    According to Wired.com, the banknote detection code in 
    these applications, called the Counterfeit Deterrence 
    System (CDS), was designed by the Central Bank 
    Counterfeit Deterrence Group and supplied to companies 
    such as Adobe as a binary module. However, 
    experiments by Steven J. Murdoch and others showed that 
    this banknote detection code does not rely on the 
    EURion pattern. It instead detects a digital 
    watermark embedded in the images, developed by 
    Digimarc.

http://en.wikipedia.org/wiki/EURion_constellation

An interesting hack is that this Digimarc pattern could be used for a Copy Attack [1]. To my knowledge the mark is not tied to the image of the bank note in any way. So in short: You could extract the Digimarc pattern and apply it to any other document, which then in turn could not be edited by mentioned software.

[1] https://en.wikipedia.org/wiki/Copy_attack