One of the things explained by the exhibit organizers:  portraits were compared by them to journals, a communication to posterity from those who could afford the cost.  

To trace a line backwards allows this surmise:

–blogs are like journals

–blogs are like portraits

Portraits, journals, and blogs are devoted to an image of the self or to recording and framing those impressions around which a self forms in the world.

What was once confined to the aristocracy (certain modes of communicating the self in its image world) are now taken up (and cheapened) by the bourgeoisie –first in journals and today in blogs.