You can make it so the people who don't know a lot about the web or computers can't by disabling "Right Click" as the standard user would right click and choose Copy / Save picture as..

You can also watermark your images so that nobody can see the watermark until you alter the contrast / brightness using a program.. It's ultra hidden this way and they will not attempt to remove it which means a harder hit when you catch them.

I suppose you could get your pictures copyrighted too, IT won't deter the normal user but this would deter people who know about the web and images.. They won't be stupid enough to take / use them..

I think by submitting them to sites such as Deviant art you can choose these certain copyright tasks..