Any means of disabling right click can be easily defeated by a knowledgeable person...
Once a user has had a picture displayed on their screen - it is already on their computer for the taking - as is the html source that points them directly to the picture.
You can use the transparent overlay allvip referred to... (Config Option)
You can use watermarks to make theft more difficult... (Config option)
You can mask or encrypt the url used to access the pictures so they cannot see your albums directory structure and try to 'find' full size images... (Mask Url Plugin - http://forum.coppermine-gallery.net/index.php/topic,78168.msg378273.html#msg378273
With all of these - any image displayed is still stored on the users computer.
The only way to prevent that is to not place it on the www.