Staircase at the Courtauld. Source: Mike Peel via Wikipedia.
Courtauld Institute of Art
Paul Laib negatives: over 20,000 negatives of works by British artists, 1900-1945. Includes images of many works in progress. No start date for digitisation yet.
Paul Mellon Centre for Studies in British Art
The Centre's offers major collections of images of British art. Many images are online. Others, originally collected by the Tate Gallery, exist offline at the Centre's Bedford Square address. These offline images can be searched via the Centre's library catalogue.
Warburg Institute
A unique collection of photographs documenting the icongraphical tradition in Western art. See our information about the Warburg library for how to access. Some of the collection is available as online images. The Menil Archive of the Image of the Black in Western Art is not online, though an index is available.
Most archives will also contain rare, often unique, images.