Ask HN: Easiest way to watermark everything as if it were currency

Background: http://www.cl.cam.ac.uk/~sjm217/projects/currency/

I'm working on a project where I think it would be interesting to make it take more effort for people to scan/copy/photoshop the images and documents produced by my program.

Basically I want to trip the currency detection heuristics with things that aren't and don't look anything like currency.

Any suggestions?