Hide Media Files from Search Engines

Hi everyone,

On my wordpress site I display the pictures of my products using the Foogallery plugin. As I only want to share the pictures with certain people, I have put passwords on the pages on to which I have made the Foogallery galleries. Now everything works fine, but the problem is that each WordPress media file has its own URL, and if one can find that URL, one can access the pictures without going through the password protected pages. Sometimes these URLs show up on search engines, when searching my site. How can I put a password on these URLs of media files, or prevent them from being so easily accessible? Hope it makes sense

Thanks,
TheRealCJ96