use OpenCV API to find face from video steam

find_face_by_video.py

#!/usr/bin/env python

import cv
import cv2

window_name = "preview"
load_model = "haarcascade_frontalface_default.xml"

cv2.namedWindow(window_name)
vc = cv2.VideoCapture(0)

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

haar = cv2.CascadeClassifier(load_model)

while rval:
    detected = haar.detectMultiScale(frame, 1.2, 2,
                                     cv.CV_HAAR_DO_CANNY_PRUNING)

    if detected is not None:
        for (x,y,w,h) in detected:
            color = (0,255,0)
            cv2.rectangle(frame, (x,y), (x+w,y+h), color)   # draw rectangle

    cv2.imshow(window_name, frame)
    rval, frame = vc.read()

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

vc.release()
cv2.destroyAllWindows()