ITK objects
ITK is the Insight Segmentation and Registration Toolkit - http://www.itk.org
It is a C++ library with Python bindings, and with an open-source, Berkeley-style license.
For now, here are some links:
ITK image file format compatibility
Interactive ITK application to allow you to use ITK interactively - this gives you a feel for what it can do.
Presentation on using ITK with Python (and VTK, a little bit)
