Any pointers on where to look for getting the game to output a PNG? Is this possible cross-platform? I'd like to be able to upload a PNG image to the listing server directly rather than having to upload binary data and then transform it at the other end.
The server does not do this, as the default binary is not liked with libpng. Can be changed of course. Still you would have to program a 256 colors to PNG output. For 16 bit see the code in branches for makeobj.