I’ll try to explain by example.
At 3 o’clock
Engaging reportage such as the work of Bresson, Klein, Wessing, Goldin, Parr, Capa, etc.
‘War’ reportage is a typical example but of course not covering the whole.
At 6 o’clock
Abstract tendencies such as the work of Pierre Cordier, Vik Muniz, Jurgen Klauke, Jan Dibbets, Luigi Ghirri.
This work explores the materiality of ‘a Photo’ and the suitability to reflect a subject.
At 9 o’clock
Surreal work such as Mapplethorpe, Dieter Appelt, dirk Braeckman, Araki,...
At 12 o’clock
Work not made by the author but used to make the viewer think about the exhibit. Such as Bolstanski, Marcel Broodthaers, Michael Snow, Thomas Hitschorn, Joan Fontcuberta,....
The transition from 3 to 12 is about the content
From 3 to 6 is about form
From 9 to 6 about the object
From 9 to 12 is about the subject
Googling the artists in the example clarifies a bit.