For the commissar haven't painted the coat lapels and collar insignia yet - too many conflicting sources from the web and haven't pin-pointed the right one
The commissar is no different from the other officers of his military unit, except the star on his sleeve. But megaphone - absolutely unnecessary details.

Sleeve insignia of political leaders of all ranks (from sergeant to general)
Commissars (political instructors) in infantry units. The color of the strip on the cap and the buttonholes on the collar is crimson.

Commissars in units of the NKVD (internal troops). The color of the strip on the cap and the buttonholes on the collar is a maroon.

Commissar of the artillery unit (uniform for areas with hot climates - Caucasus, Central Asia). The color stripes on the cap and the tabs on the collar - black (buttonholes - with red piping).
By the way, in 1943 (together with the introduction of shoulder straps) the position of the commissioner was abolished and, accordingly, these signs disappeared. Your officer has shoulder straps, which means he should not have any special differences on the uniform. And the buttonholes on the overcoat began to look like this:
