Officers also wear helmets in combat and normal soldiers also had a Schirmmütze (with slight differences not easily seen on b/w photographs).
The main difference is the collar insignia and the shoulder strap which indicates the exact rank
Enlisted collar. Shoulder strap in combination with rank chevron indicates rank
A Non commissioned officer (Unteroffizier). Different collar, shoulder strap
Officer.. Different collar insignia, different shoulder strap
Here on my site you see what insignia shows which rank
Additionally the officer tunics were tailored a little bit different and of better quality.
http://chrito.users1.50megs.com/uniform ... iforms.htm