License, verbatimCC0
The Metropolitan Museum of Art: Open Access, Creative Commons Zero (CC0). Flagged isPublicDomain=true in the museum's own record.
Francesco Polanzani. Portrait of G.B. Piranesi in imitation of an antique bust, from "Opere varie di Architettura, prospetive, grotteschi, antichità; inventate, ed incise da Giambattista Piranesi Architetto Veneziano" (Various Works of Architecture, perspectives, grotesques, and antiquities, designed and etched by Giambattista Piranesi, Venetian Architect), 1750. The Metropolitan Museum of Art.