The way you wanna do that when your using Photoshop is:
Make a new empty layer.
Select it, (I would suggest using ctr+a)
Right click. Somewhere below it should say "Stroke"
Click that. Mess around with the options.
Done.
If you want to add some effects to the border. Right click on the layer, "blending options. And mess around with that.
Allso, i'd suggest you pick annother character, since Ironman's grown quite famous these days, everyone knows who he is. Meaning, alot of people will use him.