Sourcing images advice

It's important for teachers to hold themselves to high standards when it comes to using the intellectual property of others. Students will not respect copyright laws if their teachers do not.

Creative Commons is a wonderful image resource for both students and teachers:http://search.creativecommons.org/
Morguefile is a terrific website with free high resolution digital stock photographs and reference images.

These two sites from Wikipedia are very valuable:
A list of sites with Public Domain images
Wikimedia Commons: a fantastic source of images that are public domain
(great for historical figures pre 1920's).

plasq also provides a clipart package of cartoon characters which are handy for story telling comics. They are available here.