Take a look at the plugin code and examine the code inside the template tag functions. I got a list of authors, then as I looped through them I was able to display their thumbnails like so:
echo userphoto__get_userphoto($author->ID, USERPHOTO_THUMBNAIL_SIZE, '', '', array(), '');
If you wanted fullsize it would just be a matter of changing the code a little. Hope this helps someone.
