While each professor may have a different preference for what information you will need for an image citation, you can use this as a guide.
If you do not know any of these items, provide what you do know and put “unknown” for the rest.
Sometimes, it is sufficient to give just a credit line below the image, rather than a full footnote or endnote. Generally, Turabian style does not require a bibliographic citation for an image.
Try these helpful guides from other schools:
John Everett Millais. Ophelia, 1852. Oil on canvas. Tate Britain, London.
762 x 1118 mm. ARTstor.
John Everett Millais. Portia (Kate Dolan), 1886. Oil on canvas. 125.1 x 83.8 cm. Metropolitan Museum of Art, New York. ARTstor.