1. A method of detecting human motion comprising: a camera collecting video images of a secured area; extracting objects in motion from the collected images; for each extracted object determining an object size; correcting the object size for optical depth perception distortion based upon known or derived geometrical and optical information; for each extracted object determining, an object size, an object aspect ratio, an object speed and object motion path over time; extracted a signature for each extracted object by comparing the distance corrected object size with a bell curve tuned to a statistical average of human size, the object aspect ratio based upon a pair of bell curves tuned to a statistical average of aspect ratios of human proportions including one for walking and one for crawling, the object speed with a pair of bell curves tuned to a statistical average of travel speeds of a typical human including one for walking and one for crawling and object motion path travel as measured against absolute distance traveled over time; determining a respective threat probability for each of the extracted object signatures based upon the corrected object size compared with the bell curve tuned to human size, the aspect ratio compared with the bell curves tuned to both walking and crawling, the object speed compared with the bell curves for walking and crawling and upon a time of sustained object direction of travel; summing the respective threat probabilities for each extracted object signature based upon size, aspect ratio, speed and time of sustained travel; and generating a motion alert upon detecting the summed human motion threat probabilities exceeding a programmable threshold value.