You can cut the image in some parts that are touching and producing the whole picture. That way the user will loose his interest to try to right-click save the image.
And many people stop trying after the first failed attempt to copy an image.
Other than that the PrintScreen button works almost everywhere except for video streaming. (not flash-based)
You can try to open a movie with MediaPlayer classic for example and try hitting the PrintScreen button - the clipboard has black screen instead a shot of the movie in it.
May be there is a way to use this in your case.
edit:
Here's another suggestion but is it's not that technology independant.
I think that you can create a special restricted .pdf file that doesn't allow copy of both files and text.
Not sure about PrintScreen again.