As an imaging prevention method for interfering unauthorized imaging of a number of visual images projected on a screen, there is employed a method for projecting infrared light to a viewer/audience direction from at least one or more infrared light projector devices disposed at a rear side of the screen. According to the method, an amount of infrared light is directly incident into an imaging apparatus whereby increasing the prevention effect causes more infrared light to be directly incident into the imaging apparatus of a person conducting the unauthorized act.