Why the general-purpose route disappoints, specifically

Almost everyone tries the same thing first: a general chat model, one photograph, a request for a professional headshot.

What comes back

A plausible portrait of a person. Not a consistent likeness of you.

The reason is architectural rather than a matter of quality. From one photograph there is nothing to learn about what is constant in your face across angles, expressions and light — and that constancy is exactly what a portrait has to preserve.

What a dedicated system does differently

It trains on a set of your photographs specifically to separate what is stable about you from what is circumstantial. That separation is the product.

Why the distinction is worth knowing

Because people conclude from the general-purpose attempt that the whole category does not work. It does; they used the wrong shape of tool.

And the input still decides

Different days, different clothes, different light. Fifteen photographs from one afternoon teach any system, dedicated or not, that the shirt is part of your face.