You could try ImageMick

On Sun, 17 Nov 2002 08:20:50 -0500
Brian Rose <saider@gate.net> wrote:

> Does anyone know of an image thumbnail generator? It's running on a 
> server, so I do not have many libraries installed.
> 
> What I need it to do is to read in an image file and generate a 
> thumbnail image file in the same format. It needs to take all arguments 
> on the command line because it will be embedded in a script.
> 
> Something like this..
> $ thumbs file.jpg > thumbnail.jpg
> 
> Anyone know of a package like this?
> 
> Thanks in advance.
>