import numpy as np
import cv2

face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')
cap = cv2.VideoCapture(0)
while True:
 ret,img = cap.read()
 gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
 faces = face_cascade.detectMultiScale(gray, 1.3, 5)
 for (x,y,w,h) in faces:
  cv2.rectangle(img,(x,y),(x+w,y+h),(255,0,0),2)
 cv2.imshow('img',img)  
 if cv2.waitKey(1) &0xFF == ord('q'):
  break
cap.release()
cv2.destroyAllWindows()