I'm running into an error where when I try 
from PIL import Image, ImageFilter
in a Python file I get an error stating ModuleNotFoundError: No module named 'PIL'.
So far I've tried uninstalling/reinstalling both PIL and Pillow, along with just doing import Image, but the error keeps on occurring and I have no idea why. All the solutions I've found so far have had no effect on my issue. 
I'm running Python 3.5 on Ubuntu 16.04
In my case the problem had to do with virtual environments. 
The python program ran in a virtual environment, but I called pip install Pillow from a normal command prompt. When I ran the program in a non-virtual environment, from PIL import Image worked. 
It also worked when I called venv/scripts/activate before calling pip install Pillow. So apparently PIL is not found when installed in the python root but the program runs in a virtual environment.
No module named 'PIL'