When I use appadmin to display the COMMENT table, the comment.image_id field displays the title field from the image table.
Looking in sql.log, I see that comment.image_id is an integer referencing
image.id.
image_id INTEGER REFERENCES image(id) ON DELETE CASCADE,
I was expecting to see the integer id value, but the text of the title field is
displayed.
How/why does the comment.image_id field display the text of title? What in
db.py connects those two?

