OpenCV - Diffence Image 영상차

http://www.robindavid.fr/opencv-tutorial/chapter10-movement-detection-with-background.html

http://stackoverflow.com/questions/14508190/new-to-python-opencv-motion-tracking-using-webcam-thresholding-dilate

http://blog.naver.com/PostView.nhn?blogId=pinkjea95&logNo=220772239173&redirect=Dlog&widgetTypeCall=true

http://www.pyimagesearch.com/2016/04/11/finding-extreme-points-in-contours-with-opencv/