I found myself wondering if ghosts have shadows and decided to see what I could find through researching this subject. What I discovered was that ghosts do not cast shadows but a ghost can be a shadow. Confused yet? Sorry if you are. Let me try to explain what I mean.
A ghost cannot cast a shadow because only solid objects can do that. But a ghost can be seen as a shadow. Those types of ghosts are referred to as shadow figures within the paranormal scene.
Shadow figures or shadow people have been explained through different theories within the paranormal world. One theory I found states that if you think you are seeing a shadow figure that your mind is actually filling in the blank areas to make a shape that appears to you as a human would. Shadow figures are usually seen from the corner of your eye as a quick movement. To me, this theory is discounting the existence of shadow figures and explaining them away as an over-active imagination. Therefore this theory seems too simplistic of an explanation.