Is there a way to make a cv2 videoCapture, capture the whole screen of my computer?

Question

I want to make a face detection app that could capture my hole screen and show me the results of face detection in the app I'm in mistake with capturing the whole screen of my computer I want something like this: cap = cv2.VideoCapture(WINDOWS_SCREEN)

i expected that i could just do that with a special key like: 'WINDOWS_SCREEN' but it didn't work any idea?