Your tax dollars at work! The U.S. government offers an impressive array of photos, nearly all of which are in the public domain. Here's a list of image banks we've found useful, along with a few oddball sites that are fun to browse.
Sources of Free Medical and Scientific Images
Whether you call it political correctness or accessible language, you can't deny it's a thing. The info here will help you keep up with what's in and what's out. The words you choose are up to you.