Kae Verens has a new post to his blog looking at a form of non-destructive image manipulation - using the URL of the request to determine the changes that need to be made.

The solution is to not actually create copies, but to record the changes applied to the original image in the URL of your manipulated image. When the server is asked for those URLs, it runs the manipulations on the original image and gives you back the new image. Of course, we will cache the new manipulations so this doesn't need to be done every time, but this now allows you to replace the original image, then clear the cache, forcing all the variants of it to refresh, without you needing to do it again.

A demo of the script in action is included in the post as well as a link to download the script doing the work.