Use only your original work in your project.
Get written permission to reproduce another's work.
UT's Crash Course in Copyright, especially the "Getting Permission" section
Author's Alliance: Obtaining image permissions for your book. An author's perspective
Use content licensed with Creative Commons agreements. The Search identifies content that you can use. Read about the different Creative Commons licenses. More about Creative Commons.
Use un-copyrighted, public domain material. Use Advanced Google Images Search to limit your results for images you can use.