A peer graded assignment can be graded anonymously. In this case the names (and any photos) of the students doing the grading are not shown. Only the (file) names of the submissions are used to identify the pieces of work being graded.
When the peer graded assignment is not graded anonymously, the pieces of work are shown with the names (and any photos) of the students who submitted the work. This may lead to bias in the gradings.
Note that if the teacher's grades are shown to the students these are never shown anonymously.