You can use Hotlink Protection from the Cpanel to disable it.
Hotlink protection prevents other websites from directly linking to files (as specified below) on your website. Other sites will still be able to link to any file type that you don’t specify below (i.e., HTML files). An example of hotlinking would be using an <img> tag to display an image from your site somewhere else on the Web. The end result is that the other site is stealing your bandwidth. List all sites below from which you wish to allow direct links. This system attempts to add all sites it knows you own to the list; however, you may need to add others.