Unfortunately, you can pretty much forget this. You can use a javscript to
disable the right-click, but the image will be downloaded into the browser's
cache anyways. A user can simple take a screenshot of their screen to get a
copy of the image. Basically, there's no really good way to do this as there
are more ways around a block than blocks themselves. There are tools that
say they can block doing this, but these don't really deter any but the most
casual user.
Hope this helps,
Mark Fitzpatrick
Microsoft MVP - FrontPage