If a person is determined to save an image from the web page, no one can restrict him.
But these three methods can be used to restrict a casual user from saving images.
1. Disabling the right click button : by using the oncontextmenu
eg: <body oncontextmenu="return false;"> .(It does nt need to be on the body tag. instead, it can be given to the DIV tag where the image is displayed)
Problems : IE and FF will work as intented. But opera doesnt know about the oncontextmenu. so it willnot work with Opera
2. By giving the original image as background, and cover it with a transparent gif image using <img> tag. In this way, when the user rightclicks and saves the image, the transparent image will be saved. In this way user is fooled.
3. Using Flash.
But all three are not perfect solutions. Methods 1 & 2 are easily tampered by saving the webpage to a local folder and then any can find the required image.
The flash method is also not very useful coz, there are decompilers which will save all files embedded in the flash movie.