Make screenshots of areas in selenium

screenshotter.py

#!/usr/bin/env python
from PIL import Image
import StringIO

def screenshot(browser, element, filename='screenshot.png'):
    """docstring for screenshot"""
    elem = browser.find_element_by_css_selector(element)
    loc = elem.location
    size = elem.size
    screenshot = browser.get_screenshot_as_base64()
    img = Image.open(StringIO.StringIO(screenshot.decode('base64')))

    # box = (left, upper, right, lower)
    left = loc['x']
    top = loc['y']
    width = size['width']
    height = size['height']
    box = (left, top, left+width, top+height)
    area = img.crop(box)

    area.save("images/{}".format(filename), 'png')