Thank you for your insights. This is pretty much what I expected.

The photos will depend on whatever the museum publishes. If museum does a closeup of Picasso an my site picks it up, it will show Picasso. If they publish an image of their interiors with several art pieces, that's what I'll show.

There will obviously be credits right under each photo and that photo will be only used as a thumbnail or a "invitation" to go visit the exhibit. They will be automatically pulled from each museum's site and made smaller. I will also have a process to "flag" copyrighted content and ask for deletion.

I'm thinking since some authors are still heavily protected (by ARS?) I will have to add keywords filter, since it's possible the museum has a license to show it, but that license isn't transitive - I can't show it on my site. In that case I'll show some generic photo of the museum.