install opencv

pip install opencv-python

sudo pip3 install opencv-contrib-python

curl https://elektronicavoorjou.nl/wp-content/uploads/2020/06/install-openCV.html?_t=1591714866 | bash

sudo apt-get install libopencv-dev   # ubuntu c++

download required packages from below link:
https://docs.opencv.org/4.0.1/d7/d9f/tutorial_linux_install.html

NOTE: you can download required packages by "sudo apt-get install <packages>" or 
download source code by git using above link

tags: ubuntu, c++, opencv 4 version