Sorry for the short documentation, but this code was just meant to be of personal use and show an example on how to create your own custom imagine-filters in Symfony2.
Just install it as every SF2 package by adding it to your composer.js file and run the update-command or downloading the files and adding the package in your AppKernel class.
Here's an example on how to use this custom filter:
liip_imagine:
filter_sets:
thumbnail:
quality: 75
filters:
thumbnail: { size: [120, 80], mode: outbound }
watermark:
file: %kernel.root_dir%/Resources/misc/watermark.png
placement: { position: center, resize: stretch, space: "10%" }