profile picture       
noun [ C ] uk/ˈprəʊ.faɪl ˌpɪk.tʃər/ us/ˈproʊ.faɪl ˌpɪk.tʃɚ/
 头像
an image that represents you on your profile (= information about your life, work, interests, etc. on a social networking website), usually a photograph of yourself
  When my date arrived at the restaurant, he looked nothing like his profile picture.
 Usually, you can also see a thumbnail of someone's profile picture, and a list of people they are friends with. 通常,您还可以看到某人个人资料图片的缩略图,以及他们的好友列表。 
 - More examples
 - We have a policy of real photos only as profile pictures.
 - When making or receiving a phone call, your friend's latest profile picture and status is shown on the screen.
 - Personal information such as names, profile pictures, city, networks, and friend lists were made publicly available.