Psychologists have been interested in the mirror image chiefly as a device permitting the subject to discover his/her self-representation, and semioticians have denied that the mirror image could be a kind of sign. In the present paper, our intention is to develop a framework for realising a detailed comparison between perceptual reality, as seen in a peephole, and mirror images, as well a streaming video and pre-recorded video. In the first section, we introduce the semiotic notion of sign, using precise criteria to assure that the mirror image, as used by adults, functions as a sign. In the second section, experimental studies comparing some constellations of perceptual reality, mirror images, and video strips are scrutinized, and we report briefly the results of a study which we ourselves set up to investigate the capacities of 2 year old children to understand an object choice task conveyed by means in those four kinds of media. The result suggests that continuity, which is the opposite of differentiation defining the sign, is still important for enabling the understanding of the task in children at this age.