Email 'favicon' - how do you do this?

[Russinating]

Was in an email convo with various people yesterday and one of them had what I can only describe as a favicon (below).

This is in Gmail so is this unique to that and something to do with him using Google Apps? His email is a company domain, not Gmail.

 

[GravyMonster]

It's most likely his profile pic in his Google account.

 

[Russinating]

As I thought but just wanted to check. Shame, because it does stand out!