snipplets.dev/code/Python/opencv/face-detect-realtime.py

#!/usr/bin/env python3

import cv2


def face_detect(capture):
    gray_image = cv2.cvtColor(capture, cv2.COLOR_BGR2GRAY)
    faces = face_classifier.detectMultiScale(
        gray_image, scaleFactor=1.1, minNeighbors=5, minSize=(40, 40)
    )

    for x, y, w, h in faces:
        cv2.rectangle(capture, (x, y), (x + w, y + h), (0, 255, 0), 2)

    return faces


if __name__ == '__main__':
    camera = cv2.VideoCapture(2)
    face_classifier = cv2.CascadeClassifier(
        cv2.data.haarcascades + 'haarcascade_frontalface_default.xml'
    )

    while True:
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break

        result, image = camera.read()

        faces = face_detect(image)
        cv2.imshow('Face Realtime Detector', image)

    camera.release()
    cv2.destroyAllWindows()