An aerial image is a projected image which is "floating in air", and cannot be viewed normally. It can only be seen from one position in space, often focused by another lens.

Aerial image technology was used in optical printer

Optical printer

An optical printer is a device consisting of one or more film projectors mechanically linked to a movie camera. It allows filmmakers to re-photograph one or more strips of film...

s and movie special effects photography before the advent of computer graphics

Computer graphics

Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....

 in movie production, and also for combining animation

Traditional animation

Traditional animation, is an animation technique where each frame is drawn by hand...

and live action footage onto one piece of film.