Run the code like this:

python face_detect.py abba.png

If you want to understand how the code works, the details are here:

https://realpython.com/blog/python/face-recognition-with-python/

Update: Now supports OpenCV3. This change has been made by furetosan ( https://github.com/furetosan) and tested on Linux.

To run the OpenCV3 version, run facedetect_cv3.py.