Building a save photo album

Hi People I need to build a secure photo album, in a way where only some autenticated users can see the images and the images thumbnails. Some people have given idear to put the images/file directory outside of the web server documents, but how can i then insert the images thumbnails on html page... similar to <image="/somepath/my_image_preview.jgp"> How can i do this ? or is there any other thing that i can do under php to prevent this ? Thankx people Miguel Angelo