People will still find ways to copy the image no matter what...all u have to do is highlight the page, click copy, open up paint, edit/paste. and Voila! The image is yours.
Just saying....other than that..i'd go with JL said up there. :)
I use Coppermine (http://coppermine-gallery.net/).
This let’s you auto attach a water-mark on the displayed images. It also let’s you publish pictures to the site using XP Publish (JCR)
Arles Image Web Page Creator. Have been using this for about 5+ years. It has come a long way since it first came out. Tons and tons of options, extremely easy to use. The only down side is that it ends up creating a large number of static html pages, as opposed to one html page that loads up images from a folder. But for ease of use it cannot be beat.