I have installed pillow package, and uninstall attempt with sudo pip uninstall pillow leads to this message:
Not uninstalling Pillow at /usr/lib/python2.7/dist-packages, owned by OS
Manual uninstall doesn't work, because pip writes down installed packages somewhere, successfuly blocking me from installing the package again.
This python library is important to keep Linux Mint Cinnamon running. It could be removed with sudo apt-get remove python-pil (not pip), but it would most likely break the operating system.