You can try this script: <script language="javascript" type="text/javascript"
src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js">
</script>
<script type="text/javascript" language="javascript">
$(function() {
$(this).bind("contextmenu", function(e) {
e.preventDefault();
});
});
</script>
Put it here: www.yoursite.com/admin/settings/page in the Custom head code area.
But, some other javascript code can be broken because of this code, you need to test it.
Also you should know there are many other ways to save the images from any website. It will prevent only this way of saving images
You can also look here: https://www.google.ru/?gws_rd=ssl#newwindow=1&q=disable%20right%20click%20jquery