https://card.exophase.com/epic/USERNAME.png
i.e. https://card.exophase.com/epic/x3sphere.png
That's a nice URL. I edited the form's HTML to acces some unlisted cards (figured I shouldn't advertise that), didn't know you could just use a prettier URL like that and skip the hassle.
Edit: I can't get the Xbox one to work with a gamertag with a space (%20) in it.