Source: Louvre site des collections
If you are studying art or historical periods, then the Musée du Louvre and Musée National Eugène-Delacroix have a site for you! You can search for specific pieces of art, select art by media type, search for art of specific periods and more.
I tried searching for the Mona Lisa but was coming up blank until I searched for Lisa.
Apparently, the correct name of the work is Portrait de Lisa Gherardini, dit La Joconde ou Monna Lisa.