Real life double-reading image ("Duck-rabbit")

The above picture is a real-life Duck-rabbit (right): a Gestalt psychology double reading image. I apologize that the picture is not as effective as actually seeing it, but it's the best I could do. Look almost exactly in the center of the picture. There you will see a small horizontal shadow. Is is the dark underside of a slightly projecting cantilever, or is it the shadow cast on the roof by a dormer?

Double-reading images in reality are rare. But here is one. Quack!