Help with a tattoo please.

[qqqboi person]

I would like to turn this image into an IRAY decal node to place as a tattoo on the back of one of my models, so what I need to do is have like a little bit of black gradient come out from the skull but also end preety close to the skull, like a 100 pixel gradient from the skull out that would turn from black to white to simulate something like a black canvas on the characters skin. That's all.