Lyric discussion by skippers 

Cover art for Yearbook lyrics by Hanson

I personally have always thought it was about suicide. I thought that Johnny was bullied to the point of suicide. The reason they can't forget his face is because they never did anything, never spoke up to help him. The reason Katie won't speak his name is because she knows the things she said to or about him. Maybe he died before the pictures were taken, that's why there's no picture, but no one will forget him.

My Opinion

@skippers I also think it's about bullying leading to suicide because of this verse: "sometimes I wonder if maybe we're to blame".