How to prevent the browser caching images

[Frans Knibbe]

Hello,

I would like to be able to prevent the browser caching the map images 
produced by MapServer CGI / WMS. Is this possible somehow?
I know it is possible to set "pragma: no-cache" in the HTML headers but 
that is not what I want, only the map image should not be cached.
I also know it is possible to set "pragma: no-cache" in the image 
header, this would seem a better idea. Is this possible to achieve?

Regards,

Frans