pass background images as command line arguments

[bowbahdoe]

You can use the built-in python argparse module or the click library to allow people to pass in things like the images to use for the body and for the eyes as arguments.

For example python face_track.py --background=base.png --eyes=eyes.png

This is a usability win because it lets people experiment with the functionality of the code (having eyes follow a person) with different images without having to touch the code itself.

These args can be optional, so the defaults you have will work just fine.