License, verbatimCC0
The Metropolitan Museum of Art: Open Access, Creative Commons Zero (CC0). Flagged isPublicDomain=true in the museum's own record.
Stefano della Bella. Two heads of old soldiers wearing helmets, both facing left and looking downwards, plate 10 from "The Principles of Design" (I principii del disegno), ca. 1641. The Metropolitan Museum of Art.