Dave

As far as I know of, using just HTML, there is no way of preventing users from downloading images off your web page (i.e.-using the "Save Image as.." mouse clicking).

There is a commercial product on the market that WILL handle what you are looking for. In a nutshell, essentially a Java applet. More info can be found at

http://ssi.1usa.com/Merchandise/ImageGuardian/

So, if you are looking for a solution, that is the good news.

Now the bad news. If I wanted an image bad enough off your website, what is going to stop me from doing a screen capture. Then bring it in Photoshop (or any paint application), crop out the parts that I don't need and still end up with what you are preventing me from downloading in the first place.

Hope this helps. Email me if you have any further questions.