To cite works of art using Chicago Style follow this standard, including as much of the information as you have available to you:
Artist Last Name, Artist First Name. Title of Work of Art in Italics. Date of Creation. Medium. Location of the Work. URL [if applicable]
Example:
Van Vechten, Carl. Portrait of James Baldwin. September 1955. Photograph. Library of Congress Prints and Photographs Division Washington, D.C. https://www.loc.gov/pictures/item/2004662552/