Python object tracking and optical flow in OpenCV.
Windows, from command shell (or git (bash) shell):
pip3 install opencv-python
Linux, OS X, from terminal:
sudo pip3 install opencv-python
On RaspberryPi, I also needed to do this:
sudo apt install libcblas-dev libatlas-base-dev libjasper-dev libqtgui4 python3-pyqt5 libqt4-test