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please AVOID multithreading with opencv code, esp. with the gui parts

(those HAVE TO stay on the main thread !).

global vars are EVIL, too.

again you should use a single loop only:

import cv2
import time

camip = 0

def main():
    cam = cv2.VideoCapture(0) # if you *wanted* to open2 webcams, you need 2 of those !
    if not cam.isOpened():
        return # only fools do not check !
    while True:
        ret,frame = cam.read()
        if not ret:
             return # again, only fools ...

        temp_frame = frame.copy() # else it's *really* a reference only !
        cv2.rectangle(temp_frame,(130,130),(430,430),(0,255,0),2)
        cv2.imshow("Camera 0",frame)
        cv2.imshow("Camera 1",temp_frame)
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break
main()