pip install opencv-contrib-python

from matplotlib import pyplot as plt
import cv2
%matplotlib inline

fc = cv2.CascadeClassifier("haarcascade_frontalface_default.xml")
img = cv2.imread("faces2.jpg")
faces = fc.detectMultiScale(cv2.cvtColor(img, cv2.COLOR_BGR2RGB),  scaleFactor=1.1,  minNeighbors=1,  minSize=(30, 30), flags = cv2.CASCADE_SCALE_IMAGE)
for(x, y, w, h) in faces:
    cv2.rectangle(img, (x, y), (x+w, y+h), (0, 255, 0), 2)

height, width, depth = img.shape
dpi=200
figsize = width / float(dpi), height / float(dpi)
plt.figure(figsize=figsize)
plt.axis("off")
plt.title("Результат, найдено лиц " + str(len(faces)))
plt.imshow(cv2.cvtColor(img, cv2.COLOR_BGR2RGB))