1. Websites of Museums, Libraries, and Archives
|Institutions are formally digitizing their permanent collections.|
TIP: search for art and add the term "Google" to filter out the super high res JPGs from the Google Art Project, which have been archived on Wikimedia.
3. Google Image Search
TIP: click "Search tools" then: (a) filter for "Large" size images and (b) "Show sizes". The first image has high resolution, 5872 x 4008. Try to find images whose resolution dimensions are both > 2000.