It's not all outside links that are being blocked, just links to sites that don't have SSL certificates. We started using one some time ago. Thing is, we aren't really the ones doing the blocking, browsers are. In older browsers like IE, their own security settings allow direct communication from non-secure sites on secure ones, but in more up-to-date browsers like Firefox and Chrome, their own security settings block all insecure content.
There are only 2 options. First, to have the host site get a SSL certificate, or replace the image links with fresh ones hosted on a site that has SSL.
You can tell if a site has the proper cert if their address is HTTPS, not just HTTP