If it is a group photo, alternatively you can use the Photo Tagging addon gramplet to set rectangles (that will be saved as thumbnails) for each person.
Add the Gramplet with the Addon Manager. Add the gramplet to the sidebar or bottombar of the Media category. Then undock it and activate the People category. After dragging a new rectangle, you can drag a person from the People category to the blank row in the Person column. You can also use the Select context menu option too. But the opening the Person Selector dialog means a lot of extra navigating.
