Is it possible to improve the image quality of CCTV, like they do in films?

In TV shows such as Alias or police shows, or in films, often poor quality CCTV footage is found in which a face, for example, is indistinguishable due to the poor image quality. Then, they will use the computer to 'improve' the quality of the image. Then, magically, the face or detail is perfectly clear. But can you really invent details from raw footage like that? I know it is possible to unblur an image like that paedophile's picture which interpol released. Thanks, this has irritated me since Blade Runner!