The first resource listed below (DIRC) is helpful if you are wanting to use an image that is not clearly indicated as being open-access. Note that most resources from U.S. government agencies (including images) are not copyrighted.
You may also wish to explore collaborative image/photo websites which do not have copyright/royalty restrictions such as Pixabay. Check out the butterflies photos!
Reach out with questions via email, or schedule a research consultation by clicking on the link to 'Book an Appointment'