AttributeError: 'NoneType' object has no attribute 'copy'

edit

and we have to guess the code ?

from imutils.video import VideoStream
import argparse
import imutils
import time
import cv2
import os
detector = cv2.CascadeClassifier(args["cascade"])

while True:
        # grab the frame from the threaded video stream, clone it, (just
        # in case we want to write it to disk), and then resize the frame
        # so we can apply face detection faster
        frame = vs.read()
        orig = frame.copy()
        frame = imutils.resize(frame, width=400)
this is the code snippet.

it means, you frame is invalid.

your code is also incomplete. what is vs ? did you check, if it opened correctly ?