===== GNU/Linux =====

(actually only tested in GNU/Linux Ubuntu Gutsy)

first install opencv development packages,
on ubuntu :

apt-get install libcv-dev
apt-get install libcvaux-dev
apt-get install libhighgui-dev

then get the _SOURCES_ of the pd you are using
and of the GEM or PDP that you are loading
( it might not work if the version 
is different )

then compile the externals :

cd pdp_opencv

edit the Makefile to fit your pd and PDP sources paths :

edit the Makefile and change the values for PD_DIR and PDP_DIR variables

then, compile it ::

make clean
make

and copy the .pd_linux to your externals folder ::

cp *.pd_linux /usr/local/lib/pd/extra/

===== MAC OSX (intel and powerPC) =====

first install openCV MacOS framework
   download openCV private framework from http://www.ient.rwth-aachen.de/cms/software/opencv/
   copy the provided OpenCV.framework folder in your /System/Library/Frameworks/ directory ::
        cp -Rf /Volumes/OpenCV\ Private\ Framework/OpenCV.framework /System/Library/Frameworks/

cd into the library folder ::

  cd pdp_opencv

edit the Makefile to fit your system and sources folders:

edit the Makefile and change the values for PD_DIR and PDP_DIR variables

then, compile it ::

  make clean
  make

and copy the .pd_darwin to your externals folder ::

  cp *.pd_darwin /Applications/Pd-0.40.3-extended-20080315.app/Contents/Resources/extra/ for example