Answer:
The body and the picture change roles.
Step-by-step explanation:
The except belongs to Body art/performing the Subject, written by Amelia Jones, an American art historian and curator, among many others and it discusses about the role of the body in art in different aspects.
In the excerpt, the author meant that the photography itself turns into the body, and the body becomes its own representation through this process. We can see it when she says that the body itself could be "supplementary". In a few words, the author tried to explain how the representation turns into the subject and the subject changes to be a part of it, and not an own self; the subject is supplemented through the picture.