Macworld has a nice Little Story on copywrite law, as it relates to artwork.
\"It\'s always safest to ask for permission before you make someone else\'s work a part of your own production. However, if a work isn\'t protected by copyright, you have the right to use it without asking. \"Even if a work is protected by copyright, you may still be able to use it without permission--if the way you use it qualifies legally as fair use.
Copyright law gives four general guidelines determining what constitutes fair use. First, if you\'re using a work for noncommercial purposes, it may qualify because you\'re not trying to profit from the creations of others. For instance, using a work for criticism, comment, news reporting, teaching, scholarship, or research purposes is often fair use, as it tends to foster freedom of speech.
The second guideline is that the less creative and original a work is, the more likely it is that you can use it without permission. (For detailed examples of what qualifies as original and creative work, see \"Put Your Work under Lock and Key,\" Create, July 2000.)