1. A method of detecting the occurrence of an event in a crowd, the method comprising the steps of: (a) providing video footage of the crowd, the video footage comprising a series of image frames; (b) calculating, for each of the series of image frames, a value representative of the crowd dynamics, the value being calculated in dependence on said each of the series of image frames, thereby calculating a series of values; (c) analysing the series of values to identify any discrepancies occurring in the series of values; and (d) in response to identifying a discrepancy, providing an output signal to alert an operator that an event has been detected.