What did you do?

Tried to grab a screenshot with pyautogui. This passes control over to Pillow's imagegrab.

What did you expect to happen?

A screenshot of the entire screen.

What actually happened?

The top left corner of the screen (1/4) was saved.

What versions of Pillow and Python are you using?

Python 3.6, Pillow 4.00

Please include code that reproduces the issue and whenever possible, an image that demonstrates the issue. The best reproductions are self-contained scripts with minimal dependencies. If you are using a framework such as plone, django, or buildout, try to replicate the issue just using Pillow.

PIL.ImageGrab.grab(bbox=None)
<PIL.Image.Image image mode=RGB size=1600x900 at 0x132A0D5F898>
# screen resolution is actually 3200x1800

Fix - making the App DPI Aware:
asweigart/pyautogui#33 (comment)