I often see these generated as part of class projects, e.g. students sharing their photos from group outings with each other. Mostly they generate similar observations of the same individual by each taking their own pictures but sometimes even the pictures are the same. I assume maybe only one student in the group got a picture but they all did the observation together as a group and post several instances under different user names to all get credit for the class activity. This type of duplicate is probably something best addressed via communicating the issue to the teacher instructing them, if it is possible to find out who that is.
Sometimes these types of observations are generated outside of a class context, e.g. family members or hiking buddies sharing observations with each other. There is a feature request related to that.