These repositories or Web sites offer access to royalty-free, stock or high quality images. Each site has its own terms and conditions under which the photos are licensed. Hover over the link to find out more information on the allowed uses of the photos.
These are general places to find images. For art/architecture, photography and science, scroll down.
These Web sites offer access to free clip art, but be sure to check the copyright/license restrictions on each site by hovering over the link.