I was going to make the comment that firefox now has the javascript properties feature built in but Rich beat me to it
Pioneer seem to use a clever protection thing on some images, as in on this page
http://www.pioneer-eur.com/eur/body.jsp The image top left just saves as pixel.gif
As others have said though images are easily copied, even if you cant save them you cant still hit print screen and dump the contents in the clipboard.
Perhaps a watermarking system maybe of more use