Under the assumption that the head and hands form the largest moving connected skin coloured regions in the image, tracking the head and hands reduces to matching the previously tracked body parts to the skin clusters in the current frame. Under these conditions, explicit modelling of body dynamics inevitably makes too strong an assumption about image data. Rather, the tracking can be performed better and more robustly through a process of deduction. This requires full exploitation of both visual cues and high-level contextual knowledge. Robust, real-time human tracking systems must be designed to work with a source of discontinuous visual information .
Any vision system operates under constraints that attenuate the bandwidth of visual input.
In some cases the data may simply be unavailable, in other cases computation time is limited due to finite resources. The BBN is used to probabilistically infer the body part associations over time.