Microsoft Word will create citations for you.
Citing works of art - MLA style
Cite the artist's name (if known); the title of the artwork, italicized; the date of composition; the medium of composition (for instance, "Lithograph on paper," "Photograph," "Charcoal on paper"); and the institution and city in which the artwork is located. For artworks found online, omit the medium of composition and include the title of the Web site, the medium, and your date of access.
Constable, John. Dedham Vale. 1802. Oil on canvas. Victoria and
Albert Museum, London.
van Gogh, Vincent. The Starry Night. 1889. Museum of Mod. Art,
New York. MoMA: The Museum of Modern Art. Web. 14
Jan. 2009.
ARTstor citations
Example:
Haystacks. Claude Monet. 1890. ARTstor [online]. New York: New York.
[cited 22 October 2004]. Available from World Wide Web: (http://www.artstor.org).
Many online resources have a citation feature. Look for a Cite, Cite This or Citation button on the navigation bar of the article you are viewing.
Note: Double check the accuracy of the citation after it's created.