This is great and I'd be happy to add it to my list of High Quality Collections of Digitized Art and Archival Finds[1], where I catalog sites like these, but where are the images coming from? There seems to be no information.

For example for the American artist Charles Courtney Curran, Artvee has three: https://artvee.com/artist/charles-courtney-curran/

This is more than NY Public Library with only one: https://digitalcollections.nypl.org/search/index?utf8=%E2%9C...

And the Art institute of Chicago, with also only one: https://www.artic.edu/artists/5703/charles-courtney-curran

(note there are no duplicates among these galleries!)

And the National Gallery, with zero: https://www.nga.gov/collection-search-result.html?artist=Cha...

And the Smithsonian, which has none of the above but does have his photomechanical prints: https://www.si.edu/search?edan_q=charles%2Bcourtney%2Bcurran...

Wikipedia, by the way, has several not seen in any of the above. So I'd like to know where you are sourcing these.

[1] https://simonsarris.com/art-collections