a photograph is a moment in time captured and preserved. it is the moment where the boy opens his christmas present. it is a single moment that cannot be replicated or altered (at least not hold its authenticity if this is done). Time never stops in our world but in the world of a picture time does not move at all. the moment is frozen. photographs are a very trustworthy medium as they are an exact replication of a single moment in time, however if one needed to know what happened right before the photo was taken there would be no real way of knowing. the picture can only show a small fraction of a much larger picture that is constantly moving. because time never stops it can only be preserved through things such as art and photography.