If I had this issue:
I would use a little JavaScript to start and only target the Img tags on the sites so no one could right click on the image's and copy / save them. Here's a quick snip from doing a quick search on google.
This will disable all the right clicks on anything with an image tag on your site as long as it's loaded on each page. You can alter your alert message if you choose.
<script type="text/javascript">
//<![CDATA[
function nocontext(e) {
var clickedTag = (e==null) ? event.srcElement.tagName : e.target.tagName;
if (clickedTag == "IMG") {
alert(alertMsg);
return false;
}
}
var alertMsg = "Image context menu is disabled";
document.oncontextmenu = nocontext;
//]]>
</script>Me personally, I would take this a step further and build it so, if choose to make it IP based, I would have the ability to. Just write a quick PHP script that uses functions to get the visitors IP address (their true IP) and load that onto your server. Make sure in your PHP function, you have written in the code to accept wild cards. That way you can use a specific IP like 123.321.123.12 or 123.321.* and either of these would return a positive value in your code. Based on the returned value, that will determine if the visitor can right click on the images or not. In your java script on your main site, just call for the value returned and place that in your if statement in the above code. By doing it this way, all you really have to edit is the PHP file that's sitting on your server and you can edit / make changes and load the file to your server on the fly.
They can still do screenshots and get your images, but it would be alot more work editing the images on their part. If it is still happening after you deploy something like this, You can use similar tactics like above and completely block / redirect the visitor to where ever you want. I wouldn't recommend sending them to a completely different site, just send them to a different page within your own site. A dummy page so to speak.