Well that makes about as much sense as trying to stop someone viewing your html source or right clicking to save your images.
It can't be done so there's no sense worrying about it
The entire internet is dynamic and there's no way you're going to avoid
"us knobs" trying to make it more usefull and interesting.
If you're that concerned about dynamic image scripts, or any interactive script, there's a simple solution.
Unplug your computer.
Anyway, thanks for your concern but we're not asking why the choice is lacking, only how to enable that choice
