Working draft: http://magick-uploader.herokuapp.com/
It requires FileAPI and Canvas features from your client browser, which may be polyfilled using Flash bridges, such as flashcanvas and FileReader.
Your browser does all the magic. You only need to decode the base64 data sent to your server, and save it locally.
I'm not using it on production yet, but found the current implementation pretty
straightforward. Soon I'll update it, with a real example.