Previously I posted a list of websites where students could find safe, free photos they could use in projects that were tagged as creative commons. Below is my list of similar sites for teachers. Some of the sites, while excellent, may yield more "adult" photos IF you search for them or aren't careful, which is why they didn't make the student cut- but are still awesome finds for teachers!
(Do you know of a great site I missed? Please let me know in the comments section!, This list is updated through a delicious linkroll, check back often!)