Why being painted is unlike being photographed, and why the difference still matters.
A portrait sitting is one of the oldest deliberate uses of human attention. The camera made it briefly seem obsolete. It was never obsolete.
A portrait sitting is one of the oldest deliberate uses of human attention. The Romans practiced it. The Florentines refined it. By the seventeenth century the great Northern studios had built whole social rituals around it, complete with timed visits, conversation partners, and the careful management of light. The arrival of the daguerreotype in 1839 made the sitting briefly seem obsolete. It was not obsolete. It was, and remains, a different practice with a different purpose.
A photograph captures one one-hundred-twenty-fifth of a second of a face. The face was, during that fraction, doing whatever it happened to be doing. A photographer can wait for a better fraction. A skilled one can wait for many. But the result is always a slice. It is a slice taken from outside, by an instrument that has no opinion about which slice was the right one, and a photographer's craft consists in part of choosing the slice afterward.
A sitting works the other way. The painter does not capture a moment; the painter spends hours, sometimes days, in the presence of the subject and slowly builds a likeness that is the average of many moments. The portrait that results is no single instant. It is the face the sitter wears over the course of an afternoon, distilled. It includes the way the cheek rests when the conversation lulls, the small habit of the mouth before a smile, the angle the head returns to when no one is looking. None of these survive a single photograph. All of them survive a portrait.
A camera shows you what you looked like once. A portrait shows you what you look like.
This is the practical reason that families who can afford either still commission portraits. It is also why portrait painting did not die when the camera was invented, and will not die now that every telephone contains one. The two practices are answering different questions. The camera answers, what was here. The portrait answers, who is this.
Modern commissions almost always combine a short live sitting with an extensive reference photography session, partly out of respect for the sitter's calendar and partly because the camera, used as a tool rather than as a final product, is a magnificent aid to memory. A typical commission asks for two to four hours of the sitter's actual time across two visits. The rest of the work, and there is a great deal of it, happens in the studio, with the sitter present in the form of notes, photographs, and the painter's accumulated impression.
The sitter is asked to be themselves, in clothes they like, for as long as their schedule allows, and then to leave the painter to it. This is a much smaller imposition than most first-time commissioners expect, and it produces a much larger result than any photograph they have ever sat for. That asymmetry is the entire reason the practice is still here. It will be here in another four hundred years, for the same reason.