Two close ups, and one full picture. The back of the picture says "Wien 1918" so I think it was taken in Vienna. I have a suspicion that the "K" on his cap meant k.k. Landwehr and the "70" was his regiment.
His collar is a mystery to me, however. After (and perhaps before) the war he was a civil engineer, so perhaps he was in a engineering unit? Thank you for your help.
I can't answer comprehensively, but his collar insignia denotes he was an Fänrich (Ensign, or most junior commissioned officer, almost a warrant officer or cadet officer; think "3rd lieutenant") in a machine gun unit.