matplotlib says it needs libpng15, but I have libpng16
Question: The problem is likely a configuration issue, because getting the installation
correct on Macs seems to be tricky. I'm running Mavericks and matplotlib
1.4.x, yet when I open a Python 2.7.5 shell and `import pylib`, I get this
error:

    
    
    >>> import pylab
    
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "/Library/Python/2.7/site-packages/matplotlib-1.4.x-py2.7-macosx-10.9-intel.egg/pylab.py", line 1, in <module>
        from matplotlib.pylab import *
      File "/Library/Python/2.7/site-packages/matplotlib-1.4.x-py2.7-macosx-10.9-intel.egg/matplotlib/pylab.py", line 230, in <module>
        import matplotlib.finance
      File "/Library/Python/2.7/site-packages/matplotlib-1.4.x-py2.7-macosx-10.9-intel.egg/matplotlib/finance.py", line 38, in <module>
        from matplotlib.collections import LineCollection, PolyCollection
      File "/Library/Python/2.7/site-packages/matplotlib-1.4.x-py2.7-macosx-10.9-intel.egg/matplotlib/collections.py", line 27, in <module>
        import matplotlib.backend_bases as backend_bases
      File "/Library/Python/2.7/site-packages/matplotlib-1.4.x-py2.7-macosx-10.9-intel.egg/matplotlib/backend_bases.py", line 55, in <module>
        import matplotlib.textpath as textpath
      File "/Library/Python/2.7/site-packages/matplotlib-1.4.x-py2.7-macosx-10.9-intel.egg/matplotlib/textpath.py", line 22, in <module>
        from matplotlib.mathtext import MathTextParser
      File "/Library/Python/2.7/site-packages/matplotlib-1.4.x-py2.7-macosx-10.9-intel.egg/matplotlib/mathtext.py", line 64, in <module>
        import matplotlib._png as _png
    ImportError: dlopen(/Library/Python/2.7/site-packages/matplotlib-1.4.x-py2.7-macosx-10.9-intel.egg/matplotlib/_png.so, 2): Library not loaded: /usr/local/lib/libpng15.15.dylib
      Referenced from: /Library/Python/2.7/site-packages/matplotlib-1.4.x-py2.7-macosx-10.9-intel.egg/matplotlib/_png.so
      Reason: image not found
    

I have `libpng16` installed, but not `libpng15`.


Answer: I saw a hardcoded reference to libpng15 in _png.so.  
Uninstall and install of matplotlib fixed the issue for me.

