HAARLEM, the Netherlands — Most people associate Leonardo da Vinci with his visions of beauty: the “Mona Lisa,” for instance, or his perfectly proportioned “Vitruvian Man.” But if we had been alive at any time from the 16th century to the 19th century, we would most likely have associated the Italian Renaissance master with bulbous noses, protruding foreheads and sunken chins.

Until the 19th century, nearly all of Leonardo’s famous portraits were held in private collections, and his public masterpiece, “The Last Supper,” was accessible primarily to visitors of the Convent of Santa Maria delle Grazie in Milan. His drawings often of men and women with strangely deformed or exaggerated features — which he called “visi mostruosi,” or “monstrous faces,” and which scholars call “grotesques” — were distributed widely, and avidly copied.