License, verbatimCC0
The Metropolitan Museum of Art: Open Access, Creative Commons Zero (CC0). Flagged isPublicDomain=true in the museum's own record.
Charles Germain de Saint-Aubin. The Duel (Le Duel), from Essay on Butterflies Masquerading as Humans (Essai de Papilloneries Humaines), ca. 1756–60. The Metropolitan Museum of Art.