Dave,
Thank you. It would be great to have the creation of thumbnails and potentially intermediate sized images completely abstracted into the content repository. I have spent the last hour or so hacking away at an example image in an effort to get it to show up in an xowiki instance, but I think it won't unless it is a subtype of an xowiki content type such as ::xowiki::File.
Perhaps the question I need to ask is how easy would it be to extend the functionality you have described to work on ::xowiki::File objects of mime type 'image/pjpeg'?