如果出现以下类似问题，很可能时你pip的版本不够高：
Downloading/unpacking SimpleITK
http://pypi.python.org/simple/SimpleITK/ uses an insecure transport scheme (http). Consider using https if pypi.python.org has it available
Could not find any downloads that satisfy the requirement SimpleITK
Cleaning up...
No distributions at all found for SimpleITK
Storing debug log for failure in /home/s/.pip/pip.log
所以需要你跟新你的pip版本然后安装：
sudo pip install --upgrade pip