If you cannot access it in your school there are several ways you can install it.
One way would be installing the needed package on your home computer (when windows type in 'pip install [pckg-name]')
you will find that package in your python folder->Lib->site-packages
just copy it on some usb and paste it on school computer same path
Another way would be download the package at home (directly on pypi website would be the best) and again use usb and install it then on school computer
Also you can upload that package to some webhosts (if you do not have your own domain/webspace) and use that link on your school computer in your ide or python settings as an alternative to get packages from
Or you ask some of your teachers whatever.
There are many ways to get packages installed without internet access. You can also google that e.g. 'how to install pypi packages without internet access'
Edit
http://pillow.readthedocs.org/installation.html