We present a method for hiding images in synthetic videos and reveal them by temporal averaging. We developed a visual masking method that hides the input image both spatially and temporally. Our masking approach consists of temporal and spatial pixel by pixel temporal variations of the frequency band coefficients representing the image to be hidden. These variations ensure that the target image remains invisible. In addition, by applying a temporal expansion function derived from a dither matrix, we allow the video to carry a visible message that is different from the hidden image. The image hidden in the video can be revealed by software averaging, or with a camera, by long exposure photography. The method finds applications in the secure transmission of digital information.