title: I have already installed libpng, but there is an error " 'png.h' file not found #include <png.h>" when I am installing the autopy
body: <p>I am a beginner at python, recently I want to install autopy in my Mac (Mavericks,10.9.4). 
      I read many introductions and other people's questions. But I still cannot install the autopy successfully. My steps to install the autopy are as below:</p>
  
  <ol>
  <li>I have installed the libpng from the <a href="http://ethan.tira-thompson.com/Mac_OS_X_Ports.html" rel="nofollow">http://ethan.tira-thompson.com/Mac_OS_X_Ports.html</a> </li>
  <li>I am beginner, I check the /Library/Frameworks and /usr/local and I
  think I have installed the libpng correctly</li>
  <li>[Terminal]<code>git clone git://github.com/msanders/autopy.git</code></li>
  <li>According to the introduction, I write <code>#include &lt;OpenGL/gl.h&gt;</code> at the seventh line of the autopy file "src/screengrab.c"</li>
  <li>[Terminal]<code>cd autopy</code></li>
  <li>[Terminal]<code>python setup.py build</code></li>
  </ol>
  
  <p>And here comes in the command window</p>
  
  <pre><code>src/png_io.c:3:10: fatal error: 'png.h' file not found
  #include &lt;png.h&gt;
            ^
  1 error generated.
  error: command 'cc' failed with exit status 1
  </code></pre>
  
  <p>Do I need to rewrite the file address of "png.h" in the png_io.c?And what should I do to install the autopy on Mac?Do I have some important Omissions?</p>