You can search on CC Search for items that have been intentionally licensed by the copyright owner to allow for reuse.
https://ccsearch.creativecommons.org/
If you're not finding relevant results, try using the old interface by clicking the link in the upper right corner of the page. You should see something like the image below. Select the collection you want to search. For images, I suggest Google Images, Wikimedia Commons, or Europeana. Then make sure to pay attention to the two checked boxes beneath the search bar. If you're not planning to alter the content and you're not using it for commercial purposes, uncheck these boxes. Enter your keywords in the search box and click "search" or press enter. This applies a filter to your search so that you are only searching images with a license that allows them to be reused for your intended purpose.
Fair Use is an exception to copyright law and it should only be relied upon after all efforts to secure permission have been exhausted and under very specific circumstances, in consultation with a librarian. "In its most general sense, a fair use is any copying of copyrighted material done for a limited and “transformative” purpose, such as to comment upon, criticize, or parody a copyrighted work. Such uses can be done without permission from the copyright owner. In other words, fair use is a defense against a claim of copyright infringement. If your use qualifies as a fair use, then it would not be considered an infringement." - https://fairuse.stanford.edu/overview/fair-use/what-is-fair-use/
These are the four factors that judges use to weigh fair use cases: