ITK is an open-source software toolkit for performing registration and
segmentation. Segmentation is the process of identifying and classifying
data found in a digitally sampled representation. Typically the sampled
representation is an image acquired from such medical instrumentation as
CT or MRI scanners. Registration is the task of aligning or developing
correspondences between data. For example, in the medical environment,
a CT scan may be aligned with a MRI scan in order to combine the
information contained in both.

WWW: http://www.itk.org