Wikimedia Commons is the best place to search for Creative Commons licensed images that are free to download and adapt. NOTE: All images found on Wikipedia are provided through Wikimedia Commons. DPLA and other online museums also upload through Wikimedia Commons.
The Creative Commons (CC) Search Portal works across multiple platforms, such as Openverse, Flickr, and Europeana. Not all images are licensed for reuse or adaptation. Check the CC License!
You can narrow the search to find either "Use Commercially" or "Modify or adapt" using the license section filter.
Find an image and select "Get this image"
Scroll down to "Additional info" to find the license information - you should see a link for either "All rights reserved" or "Some rights reserved." When you select the link, it directs you to the Creative Commons License for the image. You will need to link to this Creative Commons License page for your citation.