Clippix ETC's sister site - this one gives clip art images.
Run by Florida's Educational Technology Clearinghouse, Clippix allows you to find royalty-free photos.
Conduct your search, then on the top left, click on "any license" and "all creative commons" (in the dropdown menu).
Conduct search, click on "search tools", then "usage rights", and finally "labeled for reuse"
Search 12 sources of pictures, music, and videos that have creative common licenses. Enter your term in each box and click on the source you want to search.