You can use pyscreenshot module.
The pyscreenshot module can be used to copy the contents of the screen to a PIL image memory or file. You can install it using pip.

$ sudo pip install pyscreenshot

Usage:

import pyscreenshot as ImageGrab
# fullscreen
im=ImageGrab.grab()
im.show()

# part of the screen
im=ImageGrab.grab(bbox=(10,10,500,500))
im.show()

# to file
ImageGrab.grab_to_file('im.png')

This works for me:

#!/usr/bin/env python3

from PIL import ImageGrab

while True:
   px=ImageGrab.grab().load()
   m=px[613,296]
   print(m)

I think it will be faster if you just grab one pixel though by specifying a bounding box like this so you only grab one pixel:

#!/usr/bin/env python3

from PIL import ImageGrab

while True:
   screen=ImageGrab.grab(bbox=(613,296,614,297))
   px = screen.load()
   m=px[0,0]
   print(m,screen.size)