PIL support JPEG

使用Image模块出现如下错误

IOError: decoder jpeg not available

需要安装libjpeg-devel：
yum install -y libjpeg-devel

重装PIL：
pip uninstall PIL
pip install PIL

安装PIL出现如下问题：

  Could not find any downloads that satisfy the requirement PIL
  Some externally hosted files were ignored as access to them may be unreliable (use --allow-external PIL to allow).
  No distributions at all found for PIL

解决方法：

pip install PIL --allow-external PIL --allow-unverified PIL