  Online interactions are increasingly involving images, especially those
containing human faces, which are naturally attention grabbing and more
effective at conveying feelings than text. To understand this new convention of
digital culture, we study the collective behavior of sharing selfies on
Instagram and present how people appear in selfies and which patterns emerge
from such interactions. Analysis of millions of photos shows that the amount of
selfies has increased by 900 times from 2012 to 2014. Selfies are an effective
medium to grab attention; they generate on average 1.1--3.2 times more likes
and comments than other types of content on Instagram. Compared to other
content, interactions involving selfies exhibit variations in homophily scores
(in terms of age and gender) that suggest they are becoming more widespread.
Their style also varies by cultural boundaries in that the average age and
majority gender seen in selfies differ from one country to another. We provide
explanations of such country-wise variations based on cultural and
socioeconomic contexts.
