I am trying to write some data to a PNG file using C++ with Visual Studio Express 2013 on Windows 7 64-bit. I understand that to do this, I need to use an external library,
The missing header file may be because you need to specify addition include directories as well to point to libpng's header files. It looks like you are probably linking correctly.
It's been a while since I've done this in visual studios, but there should be a field for this in the projects configuration.