Hi,

This is not possible as this is a browser native feature. Anyone who loads your website have full access to the page source, including every resources loaded on your website and this is not possible to disable.

Flickr does something that Armando is requesting. It's not perfect but they do "hide" it by associating the photo to a "dummy" file.

Hm, not too sure if there's a proper way to hotlink files with php but I think it is possible on the server level but since most of you are on normal shared hosting, I am not too sure if this is even do-able :x