Creation of icons for heroes

[Dominus15]

How can I make an icon look more like the icon of the heroes they put in Warcraft... Let me explain, for example in the following link they put 2 icons, one that says "HERO" where you can see a transparent white outer layer However, the unit icon does not have that white layer. I would like you to help me or explain to me how I could add that layer to my icons.
BTNHighbornePriestess

Hero icon (white border or white layer)

Unit icon (without that layer)

Edit: The icon given as an example does not belong to me nor do I intend to own it or take the credits as such. I just put it there for demonstration.