as stated before - there's no fool-proof way to stop image theft.
However, another suggestion to make it harder for thieves: get a client application that will generate Flash movies out of your images - a flash movie that only shows one single frame in an endless loop will make it nearly impossible for non-experts to make a "right-click"/"save as", so the only option they will have then is making a screenshot - you can spoil this by using interleaving techniques.
Please understand that this trick will have some drawbacks as well:
- The app to create the flash movie will cost you some money
- You will have to learn how to use it effectively, or hire someone to do this for you
- Coppermine can't create thumbnails from flash files, so you would have to create custom thumbnails using a client app -> using coppermine will become a bit more complicated for you
Yet another option: there are desktop apps that turn one single pic into many parts and create the surrounding html for you to make the pic appear as one on the screen only. RightClick/SaveAs will only give the thief an unimportant little part of the pic. Drawbacks: still screenshots are possible; coppermine is not capable to upload the surrounding html and the single little pic parts easily.
Third option: make the pics appear as background image of a table with a transparent gif in the front (within the table cell). Will fool newbies, however the pic will exist in the browser's cache still, so experienced users will be able to steal it. Will not work in all browsers.
Bottom line: don't publish content on the internet if you're afraid of theft.