Why do Instagram Users Tag Friends in Comments?

Tagging a friend in a comment is one of the well-known mechanisms that leads user interaction in social media. This paper investigates the current practice of user tagging in Instagram by collecting a large-scale data that includes 9 K posts and their 4 M comments shared by 3 M users. Our analysis reveals that 54.8% of the comments contain user tagging, meaning that user tagging is widely-used in Instagram. To shed light on why Instagram users tag friends in comments, we develop a learning-based model that classifies the motivation of user tagging into one of the following motivations: (i) information-oriented, (ii) relationship-oriented, and (iii) discussion-oriented. We then apply our model to the comments with user tagging in our data, and reveal that user tagging is often used for interpersonal communication with friends.