I think what he means if you viewed the source you could see where the file is coming from.
Like on vbulletin the images have a field in the database that points to a directory on the server.
@Replicators
If this is what you mean then I would just use .htaccess in the folder where the files will be stored.
I'll try to find the .htaccess
not tested but try
Save file as
.htaccess (nothing more, nothing less.)