An image processing system configured to receive a first stream of images at a first resolution from a first image source with a field of view of an environment and a second stream of images at a second resolution lower than said first resolution from a second image source with substantially the same field of view as said first image source, said system comprising: a localizer component configured to provide a location for any object of interest independently of class within successive images of said second stream of images; a classifier configured to: receive one or more locations selectively provided by said localizer, identify a corresponding portion of an image (17-N) acquired from said first stream at substantially the same time at which an image from said second stream in which an object of interest was identified and return a classification for the type of object within said identified portion of said image from said first stream; and a tracker configured to associate said classification with said location through acquisition of successive images in said second stream; characterised in that: said localizer is adapted to receive inputs from a plurality of previously acquired images of said second stream when analysing a given image of said second stream; an interval (K1-K4) between successive pairs of said plurality of previously acquired images and said given image is relatively short when tracking objects detected as moving quickly across the field of view of the environment, and said interval is relatively longer when tracking objects detected as moving slowly across the field of view of the environment; and said interval is of varying length when tracking a plurality of objects detected as moving at varying speeds across the field of view of the environment. a localizer component configured to provide a location for any object of interest independently of class within successive images of said second stream of images; a classifier configured to: receive one or more locations selectively provided by said localizer, identify a corresponding portion of an image (17-N) acquired from said first stream at substantially the same time at which an image from said second stream in which an object of interest was identified and return a classification for the type of object within said identified portion of said image from said first stream; and a tracker configured to associate said classification with said location through acquisition of successive images in said second stream; characterised in that: said localizer is adapted to receive inputs from a plurality of previously acquired images of said second stream when analysing a given image of said second stream; an interval (K1-K4) between successive pairs of said plurality of previously acquired images and said given image is relatively short when tracking objects detected as moving quickly across the field of view of the environment, and said interval is relatively longer when tracking objects detected as moving slowly across the field of view of the environment; and said interval is of varying length when tracking a plurality of objects detected as moving at varying speeds across the field of view of the environment. said localizer is adapted to receive inputs from a plurality of previously acquired images of said second stream when analysing a given image of said second stream; an interval (K1-K4) between successive pairs of said plurality of previously acquired images and said given image is relatively short when tracking objects detected as moving quickly across the field of view of the environment, and said interval is relatively longer when tracking objects detected as moving slowly across the field of view of the environment; and said interval is of varying length when tracking a plurality of objects detected as moving at varying speeds across the field of view of the environment.