They mention this was "discovered three years ago", but I was sure I remembered this from years back.
"Adobe adds algorithms to Photoshop that prevent users from opening or printing scanned money. While we've been aware of this feature for quite a while" Posted by Craig Swanson on May 14, 2006 07:03 PM http://www.creativetechs.com/iq/how_to_use_scanned_money_in_...
edit: seems to be more info here, from 2004. Latest Photoshop version contains anti-counterfeit measures http://www.geek.com/news/latest-photoshop-version-contains-a...