1. A method of tracking an object captured by a camera system, the method comprising: receiving image data representing first and second images of a field of view of the camera system; detecting a first object captured in the first image and a second object captured in the second image; producing a first signature of the first object and a second signature of the second object, the first signature representing a first set of features of the first object and the second signature representing a second set of features of the second object; producing data derived from the first and second signatures, the data corresponding to a first subset of features selected from the first set and a second subset of features selected from the second set; and analyzing the data to determine whether the second object is an instance of the first object.