Image citations follow the same basic format as other citations. The artist is considered the author of the work. Include the medium of the work in brackets following the title of the work. A museum where a work is housed would be similar to a publisher for a citation, and will include the location of the museum.
More detailed information and examples can be found in section 10.14 of the manual.
Artist's last name, Artist's initials. (Year). Title of the Work [Medium of composition]. City where the work is located or held: Name of institution where work is housed or name of collection.
Da Vinci, L. (1503-1519). Mona Lisa [Painting]. Paris, France: Musée du Louvre.
If the art is only viewed online, replace the location information with the URL:
Da Vinci, L. (1503-1519). Mona Lisa [Painting]. http://www.louvre.fr/en/oeuvre-notices/mona-lisa-portrait-lisa-gherardini-wife-francesco-del-giocondo
If you are citing an artwork found in a book, cite the book only. Your in-text citation will include the page number to direct your reader to the artwork.
Use the same format as you would for a standard web source.
Airwolfhound. (2011, February) Squirrel - Explored :-) [Photograph]. https://www.flickr.com/photos/24874528@N04/5463003690/