Decompiling flash graphics

I am about to develop a system that will allow registered users to download some hefty maps in a series of swfs. That is they will be seperate swfs each providing different layers of a map, that the user can navigate in and edit. My worry is that they can take the swfs that are in their cache, decompile them, extract the graphics and recompile them. I cant imagine there is a surefire way to protect graphics from copyright enfringment in FLASH, but does anyone know a good technique for making it difficult enough to discourage most hackers?

all the best,

Stanford