A very useful site for finding copyright free photos is Pics4Learning.
Remember, you must still link back to the website page where you found the picture or photo.
Here is an example.
http://www.pics4learning.com/details.php?img=barrierreef-043.jpg
Coral of Great Barrier Reef
This would appear in a bibliography if used in a piece of information.
Davidson, Hall. barrierreef-043.jpg. May 2004. Pics4Learning. 26 Jul 2013 <http://pics.tech4learning.com>