1. Method of detecting a fire in a scene by infrared radiation image processing, said method comprising the steps of: receiving a sequential plurality of infrared radiation images of the scene, each said image including an array of picture elements (pixels), each pixel having a value that is representative of the pixel's portion of infrared radiation intensity in the array of the scene image; identifying a region of at least one pixel in one image of the plurality of images of the scene based on pixel values; tracking said region through images of the plurality subsequent said one image to determine a change of said region that meets predetermined infrared radiation criteria; and detecting the fire in the scene based on the determined change of said region.