The PhotoMerchant system does have a disable right-click option which is automatically enabled on all new accounts, so that visitors are unable to download the preview and thumbnail images within your site. Any attempts to save an image will only save a single-pixel GIF called kittens.gif.
You can ensure this option is active by navigating to your Website / Settings page of your admin account and checking that the Image Protection radio button is set to On.
Even with this protection, users can still take a screenshot of your webpage using the basic image editing tools that come with Windows and Mac OSX - and there is very little that can be done about that. However, any images captured in this way are only ever going to be of a low-resolution and will not be useful for print purposes. To help protect your work on this front you will want to apply Watermarks to your gallery images.
Hope this helps!