Residual Self Image is a phrase used in The Matrix to describe the appearance of someone within the simulation. As The Matrix is a trans allegory, I thought it was interesting to consider in that context.
The way you see yourself is not the same as how others see you, and I think this is especially true as your appearance changes in gender transition. Hormones can change the shape of the face and the quality of the skin, but this usually happens very slowly. That makes it hard to see the difference if you see someone everyday, although it would be clear in a photo from years ago.
I think the change is especially hard to see in yourself, because you have a model in your head of what you look like and who you are. Human perception does not show you an objective vision of what is out there - your eyes are used to update a model in your mind. This is complicated by dysphoria amplifying the older aspects of yourself and generally distorting things. The effect is you cannot see yourself as others do.
People are a sort of mirror - they try to tell you who you are. For trans people especially they are often wrong. To break out of the matrix, Neo has to pass through a mirror - a fluid and warping one. On the other side he finds he has new eyes which he has never used before.
In psychology, apperception is, “The process by which new experience is assimilated to and transformed by the residuum of past experiences” (Runes). So what do you see in the mirror? It’s, at least partly, a residual self image.