Look at the corners of the frame and notice whether they echo anything nearer the subject. Ask whether there is a section of the frame that changes your sense of the portrait when viewed on its own.

A person in a frame from the portrait series
A portrait in this collection
A portrait displayed as part of the featured selection
A selection from the portrait studies
A portrait to explore through its visual details
A portrait to spend a moment with
A portrait image from the photo series
From the gallery sequence
A portrait from the gallery sequence
A frame in the portrait collection