There is a known issue that for some reason wasn't fixed.
Issue: [https://github.com/msanders/autopy/issues/75][1]
It contains following workaround (commands to type in console):
brew install libpng
CFLAGS="-Wno-return-type" pip install git+https://github.com/potpath/autopy.git
[1]: https://github.com/msanders/autopy/issues/75