All they are doing is making you jump through a few extra hoops to get the photo. Once an image appears in a user's browser you cannot stop them from taking a copy.
As a last resort all a user has to do is press the PrtScrn (Print Screen) key on their keyboard and a copy of the screen is put into their clipboard. You then simply open a new file in Photoshop or most other other image editing applications using the contents of the clipboard. Once it is in an image editing application you can do what you like with it.
Bottom line: if it's going to cause you problems if anyone copies your web images, then don't publish them on the www in the first place.