Late reply, but I wanted to add to Kim's reply. I've also used GAMADV-XTD3 to update all students' picture to be their official school photo. It's been a minute, so I don't remember exactly the steps I took, but think I either had a csv file that GAM referenced that matched user to filename (would have probably been StudentID#.jpg), or I did a bulk rename of photos to the student's Google username (username only, not full email). I used the same photos our school photography company provides that we also use in in our SIS as person photo.
If you need, I can probably dig out the scripts I used last time and share, to have a reference to start from.