Wesley's Weekly HOW TO: Ghost Effect
Making a ghost effect is one of the oldest tricks in special effects, but before the use of Optical Printers and green screens, effects makers used a trick known as "Pepper's Ghost" in which a semi-transparent mirror was used to reflect an image of a person standing off-camera.
They would paint the space behind the actor solid black, and shine a spot light on him, and get him at such an angle that the Camera would see the ghost image transposed on the scene, but would frame out the guy standing off...
