Modern Language Association (MLA) citation style from the Purdue OWL
The Chicago Manual of Style (online). 15th ed. Chicago: U of Chicago, 1993. (Olin Reference Desk Z 253 U69x 2003; also Uris) "A standard work, thoroughly revised and updated, which serves as a how-to book for authors and editors. The basics online: Chicago Manual of Style.
Manage information effectively and efficiently using free Citation Software/PDF organizers such as Zotero or Mendeley.
This guide to not only has excellent information about citing images but also will give you an ArtStor model citation:
Also useful is Cornell's Guide to Citing Images.