import cv2

def detect(path):

    img = cv2.imread(path)

    cascade = cv2.CascadeClassifier("/vagrant/detect/haarcascade_frontalface_alt.xml")#xml文件路径一定要注意

    rects = cascade.detectMultiScale(img, 1.3, 4, cv2.cv.CV_HAAR_SCALE_IMAGE, (20,20))

    if len(rects) == 0:

        return [], img

    rects[:, 2:] += rects[:, :2]

    return rects, img

def box(rects, img):

    for x1, y1, x2, y2 in rects:

        cv2.rectangle(img, (x1, y1), (x2, y2), (127, 255, 0), 2)

    cv2.imwrite('/vagrant/img/detected.jpg', img);

rects, img = detect("/vagrant/img/one.jpg")

box(rects, img)

http://fideloper.com/facial-detection

$ sudo apt-get update

$ sudo apt-get install -y vim build-essential python-software-properties    # The Basics

$ sudo apt-get install -y python-opencv python-numpy python-scipy        # OpenCV items

$ wget http://eclecti.cc/files/2008/03/haarcascade_frontalface_alt.xml