"The Web Gallery of Art is a virtual museum and searchable database of European painting and sculpture of the Gothic, Renaissance, Baroque, Neoclassicism, Romanticism and Realism periods (1100-1850), currently containing over 44,800 reproductions. It was started in 1996 as a topical site of the Renaissance art, originated in the Italian city-states of the 14th century and spread to other countries in the 15th and 16th centuries. Intending to present Renaissance art as comprehensively as possible, the scope of the collection was later extended to show its Medieval roots as well as its evolution to Baroque and Rococo via Mannerism. More recently the periods of Neoclassicism and Romanticism were also included.
For those so inclined, this is a treasure trove of material. Enjoy!