Oooh I love postgresql's jsonb type ! I accidently set the background image for my pleroma account and didn't find a way to delete it in the interface. So I searched a bit in the database and quickly found that the column users.info contained it (quite easy).

At first, I didn't know about jsonb, so I thought it was a string and I was in for a painful REGEXP_REPLACE to remove the "background" property of the object. Then the psql interpreter complained about my trying to use REGEXP_REPLACE on a jsonb value, I read about it and realised my UPDATE would be as simple as :

UPDATE users SET info = info - 'background' WHERE id = 1;

(that's right, my id is 1, that's what you get for opening your own instance 😉)