1. A method for recognizing and tracing a gesture to provide an image sensor ( 10 ) to fetch a gesture image, the method comprising the steps of: (a) pre-processing the gesture image; (b) detecting a largest moved block of the gesture image and defining the largest moved block as a gesture block, (b1) calculating moved portions of the gesture image by utilizing an analysis of dynamic image difference; (b2) calculating a largest moved area of the gesture image by gathering statistically horizontal projections and vertical projections of the gesture image; (b3) filling empty holes of the gesture block by utilizing a dilation method; and (b4) calculating a largest connected area to detect the largest moved block by labeling connected areas; (c) analyzing a feature of the gesture block to determine the gesture block is a moved verification gesture or a command gesture; (d) determining whether the gesture block is successively changed to a moved gesture when the gesture block is the moved verification gesture; (e) detecting and tracing a center coordinate of the moved gesture when the gesture block successively changes to the moved gesture, and the moved gesture does not stop moving with duration over an action time; and (f) outputting the center coordinate of the moved gesture and re-performing the step (a).