Object Detection using only OpenCV

import cv2

from matplotlib import pyplot as plt

# Opening image

img = cv2.imread("image.jpg")

# OpenCV opens images as BRG 

# but we want it as RGB, We'll also need a grayscale version

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

img_rgb = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)

# Use minSize because for not 

# bothering with extra-small 

# dots that would look like STOP signs

stop_data = cv2.CascadeClassifier('stop_data.xml')

found = stop_data.detectMultiScale(img_gray, 

                                   minSize =(20, 20))

# Don't do anything if there's 

# no sign

amount_found = len(found)

if amount_found != 0:

    # There may be more than one

    # sign in the image

    for (x, y, width, height) in found:

        # We draw a green rectangle around

        # every recognized sign

        cv2.rectangle(img_rgb, (x, y), 

                      (x + height, y + width), 

                      (0, 255, 0), 5)

# Creates the environment of 

# the picture and shows it

plt.subplot(1, 1, 1)

plt.imshow(img_rgb)

plt.show()

Note: you have to download stop_data.xml or haarcascade_frondface_default.xml 