1. Install the package manager Homebrew. It beats MacPorts any day.

2. Go ahead and install OpenCV:

   $ brew install opencv
   

3. If all is well, it should be available at:

   /usr/local/Cellar/opencv/2.4.9
   

4. Create a symlink to the compiled OpenCV files. If you don’t mind setting up your PYTHONPATH and messing up python2 and python3 support, you may use brew link opencv. Otherwise, I recommend doing the manual symlink to your Python 2.7 site-packages.

   $ sudo ln -s /usr/local/Cellar/opencv/2.4.9/lib/python2.7/site-packages/cv.py /Library/Python/2.7/site-packages/cv.py
   $ sudo ln -s /usr/local/Cellar/opencv/2.4.9/lib/python2.7/site-packages/cv2.so /Library/Python/2.7/site-packages/cv2.so 
   

5. Check that it works!

   $ ipython
   Python 2.7.9
   [GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
   Type "help", "copyright", "credits" or "license" ...
   
   In [1]: import cv2
   In [2]: img = cv2.imread('path-to-image/helloworld.jpg')
   In [3]: cv2.imshow('Test image', img)
   

To check locations of site-packages folders:

In [4]: import site; site.getsitepackages()
Out[4]:
['/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages',
  '/Library/Frameworks/Python.framework/Versions/2.7/lib/site-python',
  '/Library/Python/2.7/site-packages']