import cv2

filename = 'pic.jpg'

def detect(filename):

    face_cascade = cv2.CascadeClassifier('./haarcascade_frontalface_default.xml')

    img = cv2.imread('pic.jpg')

    print(1)

    gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

    faces = face_cascade.detectMultiScale(gray,1.3,5)

    for (x,y,w,h) in faces:

        img = cv2.rectangle(img,(x,y),(x+w,y+h),(255,0,0),2)

    cv2.namedWindow("Image")

    cv2.imshow("Image",img)

    cv2.waitKey(0)

detect(filename)