Maybe you don’t worry about whose photo you might be stealing, whose creative flair you might be hijacking, when you right click and save an image from the web onto your computer or portable storage device – but you should.
If you do your best to be careful about such things (and kudos to you for being a more ethically enlightened digital scholar), here are two sites that can help you find images from people who want to share their creative images. For educational use, check the box to search for images you can modify or edit.
Creative Commons Search
and FlickrCC – Results appear as a collage of 36 thumbnails
Other strategies for finding images include adding “library of congress” to your search to see if they have an online exhibit about your topic that includes images in the public domain (most likely for American historical topics) , or adding words like historic photograph, archive, exhibit, or digital collection to your search to find online exhibits by other institutions like libraries (e.g. NYPL’s Digital Gallery) or historical societies.
Similarly, if there is a government agency (e.g. NASA) likely to have photos about your topic, add that agency name to your search or limit your advanced Google Image search to the gov domain (note: this will only capture some state government results, not all).