Here is a collection of about 1020 fairly high-resolution art images.
Mostly abstract/modern art, but also some figurative art and sculptures.

I really enjoy viewing these on the iPad (with retina display) in the
Fotomatic slideshow app, which can go through them in random sequence with
various transitions, displaying 4 images at a time so you get interesting
combinations.

The art was collected mostly via images.google.com and is often from
auction sites, where they tend to have high resolution images of artworks
they have on sale (Christies, Sothebys, etc.)