depth distance response based on the fact that the pixels in each pair appear to lie either both in the scene background 170 a 170 b or both in the scene foreground 160 a 160 b fig1 a and 1b illustrate two features at different pixel locations x feature f u03b81 looks upwards as such eqn 1 will give a large positive response for pixels x near the top of the body but a value close to zero for pixels x lower down the body feature f u03b82 may instead help find thin vertical structures such as the arm individually these features provide only a weak signal about which part of the body a given pixel belongs to but in combination in a decision forest they are sufficient to accurately disambiguate all trained parts as will be understood in embodiments such as the ones disclosed herein wherein the only body part being trained is the hand only reference points on the hands of the training images need to be considered and only those features or feature combinations which are best at predicting hand locations need to be considered in other implementations other body parts may be considered such as the feature 110 a 110 b shown on the shoulder of the user in fig1 a as mentioned above in order for the features to capture the desired object 39 s shape it is typically required that one.