Someone used the feature to take pictures of people in public looking especially depressed then when possible matched it to photos they had shared on social media of them looking overly happy.
Believe they had 5-10 examples in the story that covered it.
Except that you have to have that 'grave concern' face in Russia (and most of E Europe) since its a cultural paradigm. If you don't appear like you are going to a funeral at any given time point while you are in a public place, you could be taken as an unserious, unreliable person. Oppositely, you have to giggle and scream like a 5 year old when you come across a friend in a public place.
https://twitter.com/mikko/status/1014127790134882304
Sure there are number of companies scanning social media pics for face recognition, but another well know one is ClearView; one of their investors was bragging they had the app and would scan people to demo it:
Linked from https://advox.globalvoices.org/2016/04/07/the-russian-art-of...
Which was itself linked from https://www.theguardian.com/world/2016/apr/14/russian-photog...
Also, while not directly related to original post, these provide clear examples of how invasive surveillance and apps with features like this have the potential to be.