About the referer header. One of the primary uses of the referer header is to show a site whether the browser requesting a page (or an image) is already authenticated by that site. If your site is password protected, for example, you don't want someone without permission to be able to access a page. If the referer header on a request is showing the user is coming from outside your domain, the request will be refused. If the request is coming from inside the domain, that means that that browser session is already authenticated, and the request can be safely honored.
This is why one (I) may not be willing to break their browser by blocking the referer header so that I may see images posted on IMGUR. I need to be able to go to sites that require authentication.