The best technique available at this time is the "table background trick:"
In the above code snippet you must substitute the URL of your image for MYIMAGEFILE and the width and height of your image, in pixels, for WIDTHOFMYIMAGE and HEIGHTOFMYIMAGE. Also, transparent.gif must be a completely transparent GIF image, one pixel by one pixel in size. You can make a transparent GIF image using any quality graphics program. This method works by displaying your actual image as the background of a table, and displaying a scaled-up transparent image as the content of the table. The user, of course, sees your real image "shining through" the completely transparent GIF; but when the user right-clicks on the image to save it, they get the 1x1 pixel transparent GIF instead of your image. Yep, its a trick and real techies will simply download your page and get the background image from the files.