Compress images or otherwise reduce size to speed up page load

[elanid]

Right now, we download images at the same size and resolution as student groups upload them. Consequentially, the page takes a while to load. It would be great to reduce this time by reducing the size of images.

Pillow/PIL is probably the nicest way to do this as it can be easily integrated with the image-copying or image-downloading process we're already doing.