How to Install PIL in El Capitan with Pip?
This is because PIL is not setuptools compatible (https://mail.python.org/pipermail/image-sig/2010-August/006480.html) and has as such probably never been installable through pip. I think in general it should be considered deprecated in favor of Pillow which is an actively developed compatible fork of PIL.

So what you want to do is pip install Pillow, and also consider different pip usage since El Capitan like described in another thread here.