It’s the person taking the picture: “A Brocken Spectre is a large shadow of an observer cast onto a cloud or mist. So, when a person stands on a hill partially covered in mist or cloud, their shadow can be projected down onto the mist or cloud if the sun is behind them. An optical illusion then makes the shadow appear gigantic and at a considerable distance away from them. The shadow can also fall onto water droplets of varying distances, which distorts the perception and can make the shadow appear to move as the clouds alter and shift. This combines to make the disorienting effect of a giant shadow moving in the distance.”]