ROME, Nov 22 (Reuters) - A rare portrait by Baroque artist Caravaggio, privately owned since its discovery over six decades ago, is being exhibited publicly for the first time in a Roman museum. Caravaggio, whose full name was Michelangelo Merisi, is celebrated for his mastery of chiaroscuro—an artistic technique that uses stark contrasts of light and shadow to create dramatic realism. He passed away in 1610, in his late thirties, after a life marked by turmoil. The painting, a portrait of