tested in byrev.org, publicphoto.org, myg.me and more ... and is works very smoothly and well. Blogs must be updated to date, clean, and without much plugins.
htaccess rules in subfolders lead to not-working ... this is not a problem with the plugin, but the website administrator !
Images linked from other website's is not protected ... this is normal behavior. if you own that blogs/sites must protected with same plugin.
As default referer I added extra the following websites: