Yeah, I know. I don't need convincing it's a dumb idea, but the client wants it done and isn't budging. They have been told it's not possible to completely prevent, but they want it at least made difficult for the average tech-illiterate person, which is pretty much every customer of theirs. The content images they want to not be savable isn't publicly visible, it's behind a password-protected area and access is only granted to their customers.
I have implemented a solution of my own using div overlays with a transparent background, and some custom JS on the Fancybox pop-ups. This is solved.