Fair Use may not apply when reusing images in an article or book. In these instances, images that are under copyright and have no explicit allowances for reuse will generally require permission from the rights holder.
Below are some resources that contain images that may not require obtaining permission for your use:
Creative Commons and Public Domain Images
Google Image Search
After keyword searching, click Tools at the top of the results screen. Then under Usage Rights, select Creative Commons licenses. Google will search Flickr, Wikimedia Commons, as well as other creative commons-licensed content.
Health Education Assets Library (HEAL)
This search portal is supported by the Mountain West Digital Library, a collaborative of libraries, museums, and archives.