How To Extract Hostname of External Domain in Google Tag Manager

This blog post is based on the thread in GTM forum:

https://productforums.google.com/forum/?utm_medium=email&utm_source=footer#!msg/tag-manager/lupx4brLNao/tBFfN0PlBAAJ

Let's say you link an image  on your blog post to Justin Cutroni's website. Here's the image and the link that it goes to: http://cutroni.com/blog/wp-content/uploads/Screen-Shot-2013-09-30-at-10.45.44-AM.png:

In you go to GTM > Preview mode, you can now see this variable populated with cutroni.com

You can now create a trigger where:

Hostname does not equal your own website

Click URL matches RegEx jpg|png|svg|gif [in case you only want to capture image clicks to external domains - and know which domains did the traffic go to] AND click URL does not contain your own domain.

Once you have this, you can now setup an event where:

Category = Outbound image clicks

Action = {{page url}}

Label = {{External domain clicked on}}

and that's it.