As a software Dev for one of the worlds largest software companies (they shall not be named) there is no effective way to stop images being downloaded as a user can always extract the image from the site cache or view the sites source code and find the images location on the websever.
However what I would suggest, would be to modify the right click event on an image so it simply displays a pop up window or something just as frustrating and thus bypassing the menu which is displayed allowing them to select "save as" this shouldnt cause any browser issues.
