What extension for inline screenshot annotations?

I'm looking for an extension to Foswiki that would allow users to put a screenshot on a page, and then make annotations to that screenshot.

The purpose is that we want to create software specifications in the wiki. It's currently done in MS Word, in which it is of course extremely easy to paste an image and then use the graphic toolbar to add arrows, boxes, and texts.

This is what I want to recreate in Foswiki because it would give us the tremendous benefit of a revision-controlled repository. I'm sure I'm not the first one to have this idea, so there must be some "best practise" already.

What extension can I use to do this?

Ideally, it should have these traits, but I am flexible:

• runs locally in the browser
• IE7 compatible
• no local software installation necessary
• good usability (the users aren't very enthusiastic)
• ability to add arrows, texts, and box-shaped overlays/highlights
• runs inside the "edit" mode, or in a fashion similar to it
• supports the wiki's built-in revision control, and possibly even side-by-side diff comparison