In photography and cinematography, a multiple exposure is the superimposition of two or more exposures to create a single image, and double exposure has a corresponding meaning in respect of two images. Ordinarily, cameras have a sensitivity to light that is a function of time. For example, a one-second exposure is an exposure in which the camera image is equally responsive to light over the exposure time of one second. The simplest example of a multiple exposure is when two partial exposures are made and then combined into one complete exposure.
Digital technology enables images to be superimposed over each other by using a software photo editor. These enable the opacity of the images to be altered and for an image to be overlaid over another. They also can set the layers to multiply mode, which ‘adds’ the colors together rather than making the colors of either image pale and translucent.