Image

=== Moving images ===
{{See also|Film}}
"Moving" two-dimensional images are actually illusions of movement perceived when still images are displayed in sequence, each image lasting less, and sometimes much less, than a fraction of a second. The traditional standard for the display of individual [[Film frame|frames]] by a motion picture projector has been 24 frames per second (FPS) since at least the commercial introduction of "talking pictures" in the late 1920s, which necessitated a standard for the synchronization of images and sounds.{{citation needed|date=November 2023}} Even in electronic formats such as television and digital image displays, the apparent "motion" is actually the result of many individual lines giving the impression of continuous movement.

This phenomenon has often been described as "[[persistence of vision]]", a physiological effect of light impressions remaining on the retina of the eye for very brief periods. Even though the term is still sometimes used in popular discussions of movies, it is not a scientifically valid explanation.{{citation needed|date=November 2023}} Other terms emphasize the complex cognitive operations of the brain and the human visual system. "[[Flicker fusion threshold|Flicker fusion]]", the "[[phi phenomenon]]", and "[[beta movement]]" are among the terms that have replaced "persistence of vision", though no one term seems adequate to describe the process.