I can’t see how this would be legal. As a amateur photographer myself, I know that to do a commercial photo like this, to advertise a product, I’d need model releases and a potentially a property release. Neither of these are needed for editorial images or people’s own personal pictures. I can’t see the facebook could do this via the EULA, so they’d have to contact everyone identifiable in the pictures - which I suspect would mean it’s not viable for them.