cv2.namedWindow('preview')
vc = cv2.VideoCapture(0)
if vc.isOpened():
    rval, frame = vc.read()
else:
    rval = False
while rval:
    cv2.imshow('preview', frame)
rval, frame = vc.read()
key = cv2.waitKey(20)
if key == 27:
    break
cv2.destroyWindow('preview')
Displaying a webcam feed using OpenCV and Python