requirements.txt

External tools used for image shrinking.

JPEG:
* jpegtran (http://jpegclub.org/jpegtran/; included in libjpeg-progs package
  on Ubuntu)
* Jpegoptim (http://www.kokkonen.net/tjko/projects.html)

GIF (used only for optimizing animated GIFs):
* Gifsicle (http://www.lcdf.org/gifsicle/)

PNG:
* OptiPNG (http://optipng.sourceforge.net/)
* AdvanceCOMP PNG (http://advancemame.sourceforge.net/doc-advpng.html)
* Pngcrush (http://pmt.sourceforge.net/pngcrush/)

Ubuntu packages are:
* libjpeg-progs
* jpegoptim
* gifsicle
* optipng
* advancecomp
* pngcrush

CentOS packages are:
* jpegtran: libjpeg
* jpegoptim: can't find rpm on internet
* gifsicle: gifsicle package on repoforge
* optipng: optipng package in EPEL
* advancecomp: advancecomp package on repoforge
* pngcrush: pngcrush package on repoforge

Brew for MacOSX:
* jpeg
* jpegoptim
* gifsicle
* optipng
* advancecomp
* pngcrush

Alternative on MacOSX:
Install imageoptim (http://imageoptim.com) and then symlink from /usr/bin/
to all the required packages:
sudo ln -s /Applications/ImageOptim.app/Contents/MacOS/advpng
sudo ln -s /Applications/ImageOptim.app/Contents/MacOS/gifsicle
sudo ln -s /Applications/ImageOptim.app/Contents/MacOS/jpegoptim
sudo ln -s /Applications/ImageOptim.app/Contents/MacOS/jpegtran
sudo ln -s /Applications/ImageOptim.app/Contents/MacOS/optipng
sudo ln -s /Applications/ImageOptim.app/Contents/MacOS/pngcrush