ActionScript 3.0 :: Webcam Bounding Box?

I am currently in the middle of creating a project which essentially uses Flash as a type of augmented reality system. The idea behind it is that a webcam input will capture a users hand which is placed on a white pedestal (esstially creating a complete white backbround in contrast to the hand). Create a bounding box around the hand so that objects will only move in the space taken up by the hand.

The problem I am having is wondering which functions i should use to create a bounding box that will select the space that the hand is taking up in the webcam input. I have seen the function GetColorBoundsRect but it only seems to focus on one colour and it seems to be a static function instead of one that will need to constantly create the bounding box if it moves. This isn't just a motion dection but will need to detect the hand even if it isn't moving.