本来官方的说法是：The current version works on Windows only.
而且 PIL 已经好多年没更新了
怎么办？
当然是用 Pillow。已经在 3.0.0 版本支持 Windows 和 OS X。
The current version works on OS X and Windows only. OS X support was added in 3.0.0.
pip install Pillow 或者 pip install --upgrade Pillow 就可以了