..that should serve quite nicely for the right-clicky.
Additionally, you may wish to set this META tag in your headers:
..to inhibit page cacheing. Note: "Inhibit", not necessarily "stop".
And as my esteemed colleagues have already pointed out, if somebody wants a copy of a publicly posted image, there's little you can do short of what you've already done, which is not to display them at all.
Some other thoughts are contained on the 2nd page of this: