El triunfo de Galatea

This sea nymph, riding her shell across the water while tritons blow their horns, was painted in Naples around 1650. Its authorship has long been argued over. The National Gallery gives it to Bernardo Cavallino, a gifted Neapolitan who died young, probably in the plague that swept the city in 1656. Others have tied the picture to a documented commission from the Messina collector Antonio Ruffo to Artemisia Gentileschi, the most famous woman painter of the age, who was then living in Naples herself. Technical study has found a single hand at work, which sits awkwardly with the idea of a joint effort, though the paperwork and the painting still do not fully agree. Both artists were active in Naples in exactly these years, which is much of why the question stays open.