Self-portraiture involves copying the image of oneself reflected in a mirror on to a canvas standing on an easel. This was the process Poussin, Mignard and Desportes employed. Velàzquez and Le Brun used the same technique to incorporate images of themselves in the act of painting both their own portrait and those of their patrons into Las Meninas (1656) and the Jabach Family Portrait (c. 1650) even though those pictures are not (primarily) self-portraits.
To complicate an already complicated pictorial mise-en-scène, one must note that Velàzquez had to have had a mirror positioned in front of him, adjacent to the large canvas, which is not to be confused with the fictive canvas seen in the painting, on which he recorded both his own features and the royal party arrayed in front of him. At the same time, he had to represent a similar set up showing himself before the fictive portrait of the king and queen, whose images we only see reflected in the mirror at the back of the room (it is useful to know that in a period when mirrors were very expensive commodities, Velàzquez owned 10). Velàzquez painted a portrait of the Infanta that includes a portrait of himself in the act of painting a fictive portrait of the king and queen. His appears only in the actual picture; in the imaginary portrait only the king and queen, and none of the other characters, would have been depicted.
Le Brun sets himself a equally vertiginous task in the family portrait. Velàzquez depicts himself in the actual painting at work on another painting. Le Brun shows himself painting the painting he stood before, at which we look. To get himself in the picture, he depicts himself as a reflection in a mirror hanging behind the sitters. To do this, he, too, had to have had a mirror placed near his canvas, from which he copied his features on to the fictive mirror of the painting, thus creating not a mise-en-abîme, but a representation of one.
As was the case in Las Meninas, we cannot see what is on the fictive canvas represented in the actual painting, just the painter. In Le Brun’s case we might assume that the imagined family portrait on which the artist reflected in the mirror is working is identical to the actual portrait, but it, in fact, given the reversal of mirror images and the angle from which Le Brun shows himself viewing the family and the fictive painting, and the angle from which he had to have been viewing the actual painting, the unseen fictive portrait of the Jabach family could not have resembled the actual one in anyway. He has, in effect, painted the same portrait twice, in two different ways, in the same canvas, whereas Velàzquez represented two separate portraits. Both artist therefore surprised their patrons with not one, but two portraits.
Vermeer turns his back to the viewer, but shows us the canvas on which he works, which appears to be the painting we see before in a very early state. We know from documents that Vermeer owned a 16th-century Burgundian costume and we recognize the studio as his by its contents which he includes in other paintings This means the painter seen in the picture is Vermeer, whose identity is proclaimed by his art and the by place in his house where it was painted , not by his facial features. By the terms of the period definition, this is a picture of Vermeer, but not a portrait of Vermeer. This is a self-portrait of an indirect kind.
Poisson and Le Brun painted their own portraits at the request of a client who wished to have a record of his outward appearance. The fact that Vermeer d not record his own features and the fact that The Art of Painting was in his studio at the time of death suggests that he made it for hismelf.