Thumper - fast mass image thumbnail generator
Thumper is a scriptable, command-line tool to generate thumbnails of large batches of images. Compared to other tools, Thumper's distinct advantage is to fully leverage multiple CPU cores; if run on a machine with N available cores, it will run up to N times faster than on a single-core, single-CPU machine.
Thumper was originally created for the Advanced Python Newsletter, to demonstrate Python's multiprocessing module.
Thumper's source code is in the public domain.