Disables right click context menu on images to help deter leeches from glomming images.
When you added the image to WordPress you specified this behavior. When you insert an image you have to specify that you don't want to have a click on the image open the image. It is up to you to protect your images by not opening the image on a click. If you are able to click on an image to display the image in a new window, it is then outside of WordPress and can't be protected.