Yes, I know the only way to prevent image 'theft' is to not put them up there in the first place, and I know all methods have their weaknesses. But putting up an alert box when the user right-clicks acts as a reminder that the images are copyrighted. If this doesn't stop people from taking the images then OK, but it can be used as evidence that visitors were alerted to the presence of copyright in any dispute.

Plus, a lot of web-users aren't aware of the various ways around a disabled right-click - I asked some colleagues how they'd copy an image off a website if they couldn't right-click and they didn't know how. So if the code stops one person from stealing a pic then it's worth it.

Not everybody surfing the www is a web-wizard.