I just found out you can do a site:domain.com search in Google images and get a list of images on a site. It will also show images that other sites are stealing.
This is actually covered in the Google Image Search help page:
Can I do complex searches with image search using Boolean operators and other Google commands?
You can use all operators for image search that you would use in a Google text search. For example, you can use "site:" with image search to restrict your search to images on a particular website. So, to find all the pictures of lemurs at the Duke Primate Center, the query would be " site:duke.edu lemurs". You can also refine your search using the Advanced Image Search page.
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