“That was just a weird shadow.”
That is a flash-on-camera shot. There will be no shadow there.
Shadow might be the wrong term. What I am referring to is the different amount of light reflected from areas of skin that are not perpendicular to the light source. Curved surfaces can either concentrate or reduce the light reflected depending on if the surface, like this guy’s wattles, is concave or convex.
If light were to bounce back uniformly even from surfaces angled away from 90 degrees, old ladies’ faces and necks would look smooth and wrinkle-free in the light of a flash. But they don’t.
Where the skin surface is not perpendicular to the light source, it will look abnormally dark because not as much light is being relected back towards its source. Older people with loose skin typically have two main sags on either side of the windpipe extending to the jaw, and if they have had a prominent double chin it will droop as they age too, making a third flap hanging from the chin to the neck at a different angle from those on either side of the windpipe. This guy is old and his skin is droopy and the sides of the “13” are the edges of these neck flaps not reflecting 100% of the light directly back to the camera. While you interpret the areas of lower reflectivity to be a tattooed “13,” all I see are the two roughly parallel vertical flaps of skin with a few horizontal skin indentations, not the number 13 tattooed in flesh toned ink.
Tattoo artists typically don’t do designs entirely in flesh toned ink in any case.
The horizontal lines across the guy’s throat flaps are called “moon rings,” by portrait artists, and there will also be some below the collar; they appear when people put on weight in the neck. The middle prong of the “3” is part of one of these moon rings.
Now, if I were painting the guy’s portrait, I’d never use direct light like this for these very reasons...to avoid confusing the viewer’s eye.
It is a “13” as far as I can tell.