Her hair severely parted, Constanze Weber Mozart looks unsmilingly away from the camera. She appears to be staring at her feet. Next to her is Max Keller, a Swiss composer and old family friend, surrounded by his daughters and the rest of his family. In the background is a cottage with two garden-facing windows. The newly discovered black and white image is the only photograph ever taken of Constanze Mozart, the widow of the Austrian composer and genius Wolfgang Amadeus Mozart. The previously unknown print was discovered in archives in the southern German town of Altötting, local authorities said on...