1. A non-transitory computer-readable medium having stored thereon a program which, when executed by a processor, causes the processor to perform a method of matching a pose of a synthesised representation of a human or animal body to a captured image of the human or animal body, the method comprising: receiving the captured image data; determining from the captured image data a plurality of limb position estimates, each position estimate corresponding to an amount by which limbs of the body are separated with respect to each other; deriving from the plurality of limb positions an estimated gait phase of the body; applying the estimated gait phase to a basis gait model in order to provide an estimated pose of the body, the basis gait model comprising data which defines a displacement of the limbs or parts thereof from which the body is comprised with respect to a gait cycle period; and matching the estimated pose of the body to that of the synthesised representation of the body.