All of the websites below provide images that are free to use. Some images are licensed through creative commons, others are hosted on image databases that use licenses similar to creative commons, and some are in the public domain. Always look at licensing information to determine how to properly attribute your sources, if images can be used for commercial purposes, and whether adaptations or derivatives are allowed.
This guide is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.