The ImageGrab Module

ImageGrab.grab() => image

ImageGrab.grab(bbox) => image

(New in 1.1.3) Take a snapshot of the screen, and return an "RGB" image. The bounding box argument can be used to copy only a part of the screen.

ImageGrab.grabclipboard() => image or list of strings or None

(New in 1.1.4) Take a snapshot of the clipboard contents, and return an image object or a list of file names. If the clipboard doesn't contain image data, this function returns None.

You can use isinstance to check if the function returned a valid image object, or something else:

im = ImageGrab.grabclipboard()

if isinstance(im, Image.Image):
    ... got an image ...
elif im:
   for filename in im:
       try:
           im = Image.open(filename)
       except IOError:
           pass # ignore this file
       else:
           ... got an image ...
else:
    ... clipboard empty ...