You can't make something "unprintable" on a computer. If you see something on the screen you can always do a screen capture and print it. and by that means you can also "save" the image that way too. Once thing I'm asked to do a lot is disable the right mouse button so when someone clicks on your image and wants to do a "Save Images As..." a dialog box pops up telling the person that the mouse button has been disabled. If I remember correctly you can find this script on Dynamic Drive (
http://www.dynamicdrive.com).