I have just finished simple script which will generate thumbnail of
any image. It generates thumbnail on the fly and uses cache to save
resized image. You can call /thumb/photo.jpg?w=150&h=150 and get
resized version of the picture.
You can download it from:
http://www.cleverleap.com/ruby-thumbnail-generator/
It uses GD2 library.
Hopefully you will find it useful. Any comments or improvements are
welcome.