sorethumb is a Python module to process images in to thumbnails, and apply effects that may be difficult or impossible to do in the browser. Sore Thumb comes with Django intergration, but can be used with other web frameworks or in a stand-alone fashion.
Sore Thumb can be installed with easy_install:
sudo easy_install -U install sorethumb
See the following page for the full documentation:
There may be more information on the author's blog:
Here are a few examples of thumbnails rendered by Sore Thumb: