Authenticity is a difficult and taxing notion in both the digital and the analogue world. It is a retrospective and by implication dynamic notion, a reaction to whether or not we are dealing with the genuine article, that an object is what it purports to be at a moment in time and its content can be validated using available technology. It is not an end in itself like a fresh herring, but a red herring which, because of the pungent smell of the smokehouse, can put the hounds off the scent. Moreover it is not an absolute: an object that might appear perfectly authentic from one perspective may be considered to lack sufficient tokens of authenticity in another, and may later from both viewpoints be considered invalid. Content change may be ca...