1. A method of detecting objects using multiple sets of object probability data relating to different respective expected object sizes relative to the image size, said method comprising the steps of: (a) storing a list of locations in an image where an object has been detected, said list defining a probability data set and a probability value for each detected object; (b) detecting object locations in a set of object probability data as locations at which a local maximum probability value exceeds a threshold probability value and, if that location is substantially similar to a location previously stored in said list, where the local maximum probability value exceeds that relating to the previously stored location; and (c) repeating step (b) successively in respect of each set of probability data.