Images on the Web for Astronomy Teaching: Image Repositories
This guide lists and reviews 61 Web sites with catalogs of astronomical images that are useful for both formal and informal education. Some are general sites (including images covering many topics), whereas others are particular to one topic or one instrument. We briefly discuss getting started in using images, and copyright and fair use issues.
Fraknoi, A. 2008, Astronomy Education Review, 7(1), p.132–138