1) Update os system:

sudo apt-get update

sudo apt-get upgrade

2) Install dependencies:

sudo apt-get install build-essential cmake pkg-config

sudo apt-get install libjpeg-dev libtiff5-dev libjasper-dev libpng12-dev

sudo apt-get install libavcodec-dev libavformat-dev libswscale-dev libv4l-dev

sudo apt-get install libxvdcore-dev libx264-dev

sudo apt-get install libgtk2.0-dev libgtk-3-dev

sudo apt-get install libatlas-base-dev gfortran

sudo apt-get install libqtgui4

3) Install Python 3 and Pip3:

sudo apt-get install python3-dev

sudo apt-get install python3-pip

4) Install Opencv:

pip3 install opencv-python

5) Test Opencv:

import cv2

import numpy as np

cap = cv2.VideoCapture(0)

while (1):

     _, frame = cap.read()

    cv2.imshow("Frame", frame)

    key = cv2.waitKey(1)

    if key==27:

       break

cap.release()

cv2.destroyAllWindows()

References:

https://www.youtube.com/watch?v=H5nGc8uhQaw

https://www.youtube.com/watch?v=npZ-8Nj1YwY

https://www.youtube.com/watch?v=gGqVNuYol6o

https://www.pyimagesearch.com/2018/09/19/pip-install-opencv/

https://www.pyimagesearch.com/2018/09/26/install-opencv-4-on-your-raspberry-pi/

https://towardsdatascience.com/setting-up-raspberry-pi-for-computer-vision-installing-opencv-e0f973d38819

https://github.com/EdjeElectronics/TensorFlow-Object-Detection-on-the-Raspberry-Pi