opencv init

import cv2

cv2.namedWindow("preview")
capture = cv2.VideoCapture(0)

if capture.isOpened():  # try to get the first frame
    rval, frame = capture.read()
else:
    rval = False

while rval:
    # update graph

    cv2.imshow("preview", frame)  # display image
    rval, frame = capture.read()  # get next image

    key = cv2.waitKey(20)
    if key == 27:  # exit on ESC
        break
cv2.destroyWindow("preview")