This text is adapted from the Purdue OWL MLA guide:
Provide the artist's name, the title of the artwork in italics, the date of composition, and the medium of the piece. Finally, provide the name of the institution that houses the artwork followed by the location of the institution (if the location is not listed in the name of the institution, e.g. The Art Institute of Chicago).
Goya, Francisco. The Family of Charles IV. 1800, oil on canvas, Museo del Prado, Madrid.
For photographic reproductions of artwork (e.g. images of artwork in a book), cite the book in addition to the artwork. Cite the bibliographic information as above followed by the information for the source in which the photograph appears, including page or reference numbers (plate, figure, etc.).
Goya, Francisco. The Family of Charles IV. 1800, Museo del Prado, Madrid. Gardener's Art Through the Ages, 10th ed., by Richard G. Tansey and Fred S. Kleiner, Harcourt Brace, p. 939.