The BBC has teamed up with the Public Catalogue Foundation to launch Your Paintings, a digital library of paintings owned by national museums in Britain. Over the next two years, they expect to build a collection of 200,000 paintings (63,000 are available so far) from 3000 British collections. This includes major London museums like the National Gallery, Tate, and V&A, but the majority are smaller regional and municipal institutions.
At 944 pixels on the long dimension, the digital images on this site are more or less the right size for use in a Powerpoint presentation (vertical images are fine, but horizontal images are a little smaller than one would like).
You can read a BBC article about the Your Paintings project here.
For easy access anytime, I have placed a link to the BBC’s Your Paintings website on the VRC’s Online Resources page.