Your best option is to watermark all images before you upload them.
If you use Duotone or Monotone themes right click is disabled but it does not prevent anyone from figuring out how to get around it. Disabling right is not available on any other themes and will not become available as it creates a false sense of security. Anyone can find instructions on the internet and get around it in less than 20 seconds flat. What’s best is watermarking your images or not placing any images you don’t want stolen on the internet at all. This may help http://onecoolsitebloggingtips.com/2007/10/19/watermark-your-blog-images/