1. A computer readable medium storing computer readable program code for causing a computer to perform a method, comprising the steps of: receiving input video data; detecting a target in the video data; tracking the target; identifying a target as a human; and detecting a change in a posture of the human target in the video data when a change in at least one of a height or aspect ratio of the human target exceeds a predetermined threshold by determining the height or the aspect ratio of the target in a first frame of the video data; determining the height or aspect ratio of the target in a second frame of the video data; calculating a difference between the height or aspect ratio of the target in the first and second frames; detecting the change in the posture when either difference exceeds a predetermined threshold; determining an elapsed time between the first and second frames; and detecting the change in the posture when the elapsed time is below a predetermined threshold.