Python Imaging Library vs layered windows

Question

I'm using Python Imaging Library to take a screenshot and save it. I'm trying to take a screenshot of a program that uses layered windows, but it doesn't show up on the image. Does anyone know a way around this or maybe some other way to get the image into memory? Thanks

import ImageGrab
import os
import time

im = ImageGrab.grab()
im.save(os.getcwd() + "\\snap_" + str(time.strftime("%H-%M-%S")) + ".jpg","JPEG")