 They can choose whether of not they like to be publicly labeled on the image, or tell Facebook that it is not them in the picture.This user interface is a mechanism to generate "a constant stream of  verification data" to further train the network in real-time.As Mühlhoff argues, involvement of human users to generate training and verification data is so typical for most commercial end-user applications of Deep Learning that such systems may be referred to as "human-aided artificial intelligence".