I believe that cPannel has a feature where you can prevent users from downloading images unless it is also being downloaded with the page. When they try to download it they get nothing, or a dummy file that you can specify. It is called hotlinking feature. It would prevent the user from right clicking on an image and downloading it. However, they could still get it if they copied the image from the browser itself and then pasted/saved it in a file. Using the hotlinking feature would only make it more troublesome for them