Automatic image resizing

Anyone had any luck with setting up templates that automatically take an
uploaded image, resize it to an optimum level for that template, and display
only the modified version?  If so, how did you do this?  We want to allow
users/content owners to upload photos to display on a given page, but don't
want to worry about them uploading them too large, etc...

This would be the same functionality as provided by:

http://www.graphicsmagick.org/
http://www.boutell.com/gd/
http://www.imagemagick.org/script/index.php