Check out these other open access image banks online. Many of these images are copyrighted, so you are restricted in the ways you can use them (linking to them is fine, using them in coursework is fine, but if you're going to republish them you need permission)
Porter Campus
1801 Massachusetts Avenue
Cambridge, MA 02140
617-349-8070
South Campus
89 Brattle Street
Cambridge, MA 02138
617-349-8850