dyld: Library not loaded: /usr/local/lib/libpng16.16.dylib with anything php related

I suggest you run:

$ brew update && brew upgrade

Until couple of minutes ago I had this problem, too. Because I have an up to date PHP version, I solved it with:

$ brew reinstall php55

Hope that helps.

I followed the above (never a bad idea to keep up to date with brew anyhow) and still had the same exact issue:

LAPTOP:folder Username$ php -v
dyld: Library not loaded: /usr/local/lib/libpng15.15.dylib
  Referenced from: /usr/local/bin/php
  Reason: image not found
Trace/BPT trap: 5

Then figured out a simpler way:

Search for your libpng version(s) on your box:

# Requires locate & updatedb for mac os x
# See Link [1] 
LAPTOP:folder Username$ locate libpng15.15.dylib
/Applications/GIMP.app/Contents/Resources/lib/libpng15.15.dylib
/usr/X11/lib/libpng15.15.dylib
/usr/local/Cellar/libpng/1.5.14/lib/libpng15.15.dylib

Make a symlink:

LAPTOP:folder Username$ ln -s /usr/local/Cellar/libpng/1.5.14/lib/libpng15.15.dylib /usr/local/lib/libpng15.15.dylib

Try again:

LAPTOP:folder Username$ php -v
PHP 5.3.26 (cli) (built: Aug 25 2013 16:07:23) 
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2013 Zend Technologies
    with Xdebug v2.2.3, Copyright (c) 2002-2013, by Derick Rethans

1) Mac OS X equivalent of locate

It's because there's no symlinks for libpng. You need to link libpng again.

brew unlink libpng && brew link libpng

And you may get some error. I fixed that error by correcting permission. Maybe it's because of uninstalled macports.

sudo chown -R yourid:staff /usr/local/share/man/

Create link again and it'll work.