Scaling JPEG images

[Greg Hill]

In emacs-21 (running on a unix system) it's a piece of cake to 
display a jpeg image in the current buffer:

  (insert-image (create-image "rms.jpeg") (point))

But I would also like to be able to automatically scale it, e.g. to 
25% or 200% of the original size.  Anyone know a quick and easy way 
to do that?

Thanks in advance.

--Greg