We're working on a new community-driven website and one of the required features is the ability for users to crop and scale an uploaded image live in their browser.
It looks a little something like this:
The bar below the image is used to size the image and the inputs on the side are what receive the new adjustment data (displayed as text inputs for the example).
You can play with the example and download the source here.
This script requires the latest Prototype and Scriptaculous libraries (it will not work on Prototype < 1.6)