just installed GD, cannot use PNG

Hello
I have installed GD and some of the other recommended libraries 
(libpng, libjpeg etc).
After installing it I tried to compile the basic example(http:// 
www.boutell.com/gd/manual2.0.33.html#basics).

When I compile using gcc myFile.c -lgd -lpng I get an error saying - 
lpng is not specified.
So instead I tried linking the libpng.a file. But I did not have one.  
I installed using macports(a tool that downloads and compile some  
software).
So I then downloaded the source from the libpng website and compiled  
it myself.

-lpng still did not work, but at least I had a libpng.a file. So I  
passed the path to it to gcc. This time I did not get any error  
message, but the PNG file generated by the example cannot be opened.  
Do you guys have any suggestion on how this can be solved? I'm out of  
ideas.

/Niklas