Medical Images and Resources - most of these sites will allow you to use their images for free as long as it is for nonprofit education purposes only. Please check their licenses and cite appropriately or their generosity will more than likely disappear and this will have a negative effect on health education. You are responsible for your actions and your actions (honesty) impact the community! Be honest.
Welcome Trust Medical Photo Library
MedPix
University of Nebraska List of sites
Weill Cornell Medical Library directory List of sites