Happy to know that you like cropping tool and that you find it useful. I agree fully with keyword "temporary": time is always laking, but we see two ways to develop it, to convert such temporary trick into definitive, separated files:
1. to use coordinates of image relative to image page to crop original image, or source high-definition images of the page, by a bot script;
2. to build a "canvas environment" to edit them (filtering, resizing....) interactively by users and to save the result locally or upload them into Commons in a simple way.
We are presently exploring
archive.org environment to discover how take advantage of any derived file by that marvellous website (djvu.xml, abbyy.xml, high-resolution zipped images....).
Alex