You may want to try searching for an image in print. This could give you more information about an image by letting you view it in the context of a book or article. Here are some reference books that may be of use to you--you can look them up in the catalog.
World Painting Index by Patricia Havlice Pate, 1973-2003.
International Guide of Art Experts, Specialists, and Catalogues Raisonnes by D.M. Klinger, 1993 or
Art Books: A Basic Bibliography of Monographs on Artists by Wolfgang M. Freitag, 1997.
Index of Medieval Art.
Oxford Guide to Classical Mythology in the Arts, 1300-1900s by Jane Davidson Reid, 1993.
Dictionary of American portraits by Hayward Cirker, 1967.
Index to Reproductions of American Paintings by Lyn Wall Smith, 1977.