mac 安装PIL

PIL是python Image library
在mac终端中通过以下命令安装：

# download
curl -O -L http://effbot.org/media/downloads/Imaging-1.1.7.tar.gz
# extract
tar -xzf Imaging-1.1.7.tar.gz
cd Imaging-1.1.7
# build and install
python setup.py build
sudo python setup.py install
# or install it for just you without requiring admin permissions:
# python setup.py install --user