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:
Citing an Image (Vanderbilt)
Citing Images (U. of Cincinnati)
Citing Images (U. of Dayton)
Citing a Work of Art (R&D Online)
Tip sheet with example (PDF from chicagomanualofstyle.org)
John Everett Millais. Ophelia, 1852. Oil on canvas. Tate Britain, London.
762 x 1118 mm. ARTstor.