Macintouch has some interesting commentary on anti-counterfeiting measures that Adobe quietly slipped into Photoshop CS. The program now detects images containing currency and prevents you from working with them, even though doing so is perfectly legal, as long as you don’t then make a printout that’s double-sided or very close in size to the original.

[Tim Wright] It would be fairly easy to create other documents which would mistrigger this pattern [described in eurion.pdf].
Now the cat is out of the bag, I fully expect this to start appearing on magazine page backgrounds, books, any documents considered “sensitive”, grocery coupons, etc, which will rapidly render colour photocopiers pretty useless until they disable this feature.
For more amusement, why not put it onto t-shirts or baseball caps, which will neatly prevent people from printing (or editing) photos of you? I’m sure more inventive people will be able to think of plenty of other uses, like car decorations, wallpaper, badges and so on…