Page 49 of the MLA Handbook demonstrates how to create a works-cited-list entry for an artwork viewed firsthand at a museum. Include the name of the artist, the title of the work, the date of composition, and the name of the museum along with the city in which the museum is located:

Bearden, Romare. The Train. 1975, Museum of Modern Art, New York.

The medium of publication and materials of composition, if important to your discussion, could be included at the end of the entry as optional elements.

If you viewed the same painting on the museum’s website, include the name of the website as the title of the container, followed by the publisher of the website and the URL. Following page 42 of the handbook, omit the publisher’s name if it is essentially the same as the title of the website:

Bearden, Romare. The Train. 1975. MOMA, www.moma.org/collection/works/65232?locale=en.

Note that in the above works-cited-list entries, the date is followed by a comma in the first example and a period in the second. In the first example, 1975 is in the publication-date slot on the MLA format template. In the second example, 1975 tells you when The Train was created, not when it was published on the site MOMA. It thus appears in the optional-element slot after the element to which it relates (see the MLA Handbook 50–53 for more). There is no date after the title of the container (MOMA) because the date the image was posted is not given on the site.