1. A camera system comprising: video analytics for processing image data representing an image of a field of view projected on an image plane of an image capturing device, the video analytics comprising: an object classification module including an object classifier that is operable to classify objects captured in the field of view based on the image data, wherein the object classifier is operable to classify objects as members or non-members of an object class; and a calibration module connected to the object classification module for estimating representative sizes of members of the object class, the representative sizes corresponding to different regions of the image plane, wherein the calibration module is operable to automatically update the representative sizes in response to classifications performed by the object classifier during live operation, and the calibration module is operable to supply information representing the updated representative sizes to the object classifier to improve its object classification performance.