There's no foolproof way to do this, whatever you do can be bypassed. The moment the image is sent to the user's browser, it's on their machine and they can even choose to raid their temporary files folder. They could even take a screenshot and save that, so on and so forth.

You may have seen this on flickr. Look at this example:

http://www.flickr.com/photos/pink_farasha/4343280482/

Right clicking on the image doesn't let you "view image" or "save image". What they've done is they've created a div on the page and set the background image of the div to be the actual photo that you're seeing there. So if you then disable JS, and right click view image, you get a spaceball.gif. So that's a DIV, with a spaceball.gif in it as an <img> and the actual image as a background. The DIV has an ID of #photoImgDiv434328048 which, in the CSS, points to the actual image.

There are other options like disabling right click, as you said, but it's up to you how far you choose to go.