Citing images in MLA style is tricky, but if an image caption contains all necessary information including the image source and credit information then there is no need to include images in a bibliography.
For more information, MLA Handbook, 9th edition, pg. 8
Image From an Electronic Source (non-repository)
|Fig Number. Artist/Creator. Title. Date. Materials. Measurements, Repository/location. Source, Access Date, URL/DOI. Credit Line.|
Fig. XI. Alice Neel. Harold Dyker. 1971, oil on canvas, Artists Collection. Reed Digital Collections, 12, April 2017, rdc.reed.edu/i/00bc7844-5a14-4fa1-9aea-3cfa012d4e7f. Image © Estate of Alice Neel.
Image From the Repository
|Fig Number. Artist/Creator. Title. Date. Materials. Measurements. Repository/location. Access Date, URL/DOI (if viewed online). Credit Line.|
Fig. XI. Elizabeth Murray. Terrifying Terrain. 1989-90. oil on shaped canvases. 84 1/2 x 85 x 11 inches. Metropolitan Museum of Art, New York. Web. 12, April 2017, www.metmuseum.org/art/collection/search/485914. © Estate of Elizabeth Murray.
Image Found in a Print Source
|Fig Number. Artist/Creator. Title. Date. Materials. Measurements. Repository/location; Title of Book, contributors, publisher, page. Credit Line.|
Fig. 4. Frank Duveneck, Portrait of Maggie Wilson, oil on board, 38.10 x 30.48 cm, Museum of Fine Arts, Houston, Texas; Unsuspected Genius: the Art and Life of Frank Duveneck, by Robert Neuhaus, Bedford Press, 227. Image in public domain.