As carwiz said, there is no code to disable that. You could try covering the picture with an transparent div, so that they can't drag the image but even that is not foolproof with tools like Firebug. And of course there are screen capture tools.
The best method to deter the casual copier would be to put the image as a div background and cover it up with a transparent overlay gif of the same dimensions as the image.
<div id="image1" style="background-image: url(originalImage.jpg);">
<img src="blank.gif" height="250px" width="300px">
So, when the image is right-clicked or dragged, it will be the blank.gif that can be reached.