If you start dev_appserver.py and get this warning
WARNING 2013-10-27 01:13:08,067 api_server.py:332] Could not initialize images API; you are likely missing the Python "PIL" module.
I think it depends on the environment, but in my case http://stackoverflow.com/questions/19532125/cant-install-pil-after-mac-os-x-10-9 With reference to
xcode-select --install #install zlib?
sudo easy_install pip
sudo pip install PIL
ln -s /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.8.sdk/System/Library/Frameworks/Tk.framework/Versions/8.5/Headers/X11 /usr/local/include/X11
Even if you can install PIL, gif / png cannot be handled well if ZLIB support is not available.
--- ZLIB (PNG/ZIP) support available
Check if this is the case
*** ZLIB (PNG/ZIP) support not available