Christopher Richard Wren Ali Azarbayejani Trevor Darrell Alex Pentland Pfinder: real-time tracking of the human body. 51-59 1996 conf/fgr/1996 FG http://doi.ieeecomputersociety.org/10.1109/AFGR.1996.557243 db/conf/fgr/fg1996.html#WrenADP96