说明：  這個副程式，可以直接加在bcb的程式內，直接就能將抓取的兩張影像做相減後的結果，然後將它顯示在image上
(the subroutines that can be directly added to the bcb program, Grasp will be able to direct the two images is done by the results, which will be shown in the image on)