When zooming, does the application load the whole picture or does it just retrieves the tiles that are in the view area?

Just Tiles in the view area.

Does it use caching?

We use the browser caching, and for the server part we keep all tiles generated. There is no, by default, clean up.

What strategies can be used to scale application for very large pictures and hundreds of simultaneous users?

There is different solutions but implementation will depend of your need. Nuxeo offer a simple implementation that can be improved for:

• managing a processing queue
• pre-process different tiling size
• limit the zoom factor
• move image processing part to a dedicated server
• …

Is there support for multi-resolution formats? I noticed I cannot zoom out beyond the original size. We are going to work on really large pictures and it won't be handy to annotate at original size.

No, you are the first user that express this need. Nuxeo can implement that or you can contribute it if you feel to implement it. By the way, you can contact us (http://www.nuxeo.com/en/about/contact)

Do you have plans on supporting different annotation shapes and not only rectangles?

No client ask for it and no contributors work on it, so no :) Again, Nuxeo can implement that or you can contribute it if you feel to implement it.