EduPic Graphical Resource
EduPic Graphical Resource was launched in September 2006 by teacher William Vann as a source of free images for teachers and their students. Now with over 6000 different photographs and education illustrations, the images on EduPic are "free for use by educational professionals and the students they serve without permission."
While not as nearly extensive as a "Google image search", there are some good images here, and they are all "free."
copyright free, images