• Metropolitan Museum of Art

• Oxford Art Online
  Includes some images within the entries.
   
• The Perseus Digital Library
  A digital library of primary and secondary data on Greek and Roman literature, art, and culture.  Use the Artifact Browser to find buildings, sculptures, vases and sites.
   
• The Beazley Archive
  A research unit of the Faculty of Classics at Oxford.  The free online databae contains notes, photographs, negatives, color prints, and more.

Also, don't forget that many books, including LIMC, contain images.  If you cannot find better images online, feel free to scan these books using the scanners on the main floor of the library.

When using images, you must cite just as you do when using quotes or ideas in your research papers. It is not only important but legally necessary to give the creator or owner credit for the image just as you would a writer.

Citing a work of art in Chicago format.
(always check in your syllabus or with your professor for the required course citation style)