Pip задайте cv2 mac

pip install opencv-python

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