Film, like photography, is clearly different from earlier kinds of visual representation such as painting, and not just in the manner of its consumption and the audience to which it is directed. It has at least one material quality which makes its images members of a different order of representation: the mechanism of the camera means that it records whatever it’s exposed to automatically. In the language of semiology, the representational painting is iconic. The relationship it bears to the scene it pictures is one of similarity between chosen features, coded according to the conventions of the style employed. Umberto Eco mentions a thirteenth-century artist who claimed to be copying a real lion, and yet reproduced it according to the most obvious heraldic conventions of the time. The photographic image, however, has the guarantee of likeness, so to speak, built in, because it is not just an icon but also an index. Index is the term employed by C.S.Peirce for a sign which, while it is not produced intentionally by a human emitter, nonetheless has a human receiver, like meteorological and medical symptoms. The photograph is an index to the extent that the signifier is produced by a mechanical and chemical process. It can only be faked by some kind of trickery (which in the age of digital image processing becomes ever easier). Trick films, which make impossible things happen, were a favourite genre of early cinema, as if there were a compulsion to see how far you could go with it.