by Marina Glancy.
sure, don't forget to send 'thumbnail' and maybe 'realthumbnail' in your get_listing() function. See documentation http://docs.moodle.org/dev/Repository_plugins#get_listing.28.24path.3D.22.22.2C_.24page.3D.22.22.29 or examples in existing external repositories (dropbox, wikimedia, flickr, etc.)