Are you a crafter of icons, sounds, backgrounds and splash screens, or even window manager themes? Selecting the right license for your artwork to coexist with free software is no trivial task. Creative Commons (CC) and Free Software Foundation (FSF) licenses each have their advantages, but they are mutually incompatible. The two groups are beginning to move toward simplifying the situation, but in the meantime there are several things you can do to make license compatibility easier.
The crux of the problem is that non-software artwork like the examples above occupies a strange niche inside free software applications and operating systems. They are not code, but they are tightly integrated into the system. Artists frequently create them as standalone works, but they are also -- by necessity -- bundled into software packages and distributions, many of which are under the FSF's General Public License (GPL).