You can't stop people from stealing images from your web site because the images are downloaded to your visitor's own computer in order for it to be able to be displayed on the page. What you can do is to make it more difficult for them to take your images. This will stop some people and maybe the rest will decide that its not worth the effort.
Some of the things that you can do to increase the protection of your images do not involve HTML. You can Add a Copyright Notice into the image itself so that the stolen image will display your copyright notice. You can Protect your Images and Text with Acrobat instead of placing them in HTML pages.
Less effective is to make changes to your HTML. The following is a minor change that you can make to your JCL that moves your image into the background behind a transparent image. Should anyone use the option in the right click menu to try to save their picture it will be the transparent image that they save instead of the real image. This will not stop anyone from accessing the image directly and stealing it that way but it will slow some of the thieves down slightly and there is not a great deal of extra code required. I think that you'll find this way to be the simplest way to place a transparent image over the ones that you want to protect as the images are automatically aligned over one another.
Instead of placing the image directly into your page like this:
<img src="img/thirlmer1.jpg" width="150" height="203" alt="Image Description" />
You place a table into your page instead. The image is defined as the table background and you have a transparent image expanded to the same size as your background image as the only contents of the table. So the replacement code looks like this:
<table background="img/thirlmer1.jpg" cellspacing="0" cellpadding="0" border="0"> <tr><td><img src="img/1x1shim.gif" width="150" height="203" alt="Image Description" /></td></tr> </table>
All you will need to do is to substitute your image's filename, width, height, and description for my ones which are shown in bold in the above examples. Oh, and you'll need a copy of the transparent image to put into your table, you can get that here.
So for about an extra 100 bytes per image (and an extra 42 bytes for the transparent image) you have stopped people from being able to right click on your image in order to steal it, of course there are so many other ways that your images can be stolen but this will stop some people, just don't expect it to stop everyone.
This article written by Stephen Chapman, Felgall Pty Ltd.