Image Magick
This is an excellent free Image Conversion and
Manipulation package.
It can be used to automate the creation of thumbnails
(my "thumb.ih" download requires it).
It can be used for all sorts of purposes for example to
resize, rotate, sharpen, color reduce, or add special
effects to an image.
It could be used to create graphic buttons from an
image and some text.
It supports over 68 image formats and make no mistake this
product differs in 2 main ways from others you might find, it is
completely free and everything can be automated!
The PPWIZARD thumb nail header runs it in command line mode
but there is a GUI ('X' windows).
The source is available and it runs on Windows 2000 or
Windows 95/98 as well as on virtually any Unix system and
Linux, Macintosh, VMS, and OS/2.
It is available from
http://www.imagemagick.org/
One glitch (at least under windows), it must be
installed in the "C:\ImageMagick" directory for it to work.