On enlarging the photo to study the Mauser rifle, I noticed these features: a short military front sight base, a long tangent sight, a rather small, rounded trigger guard set well forward, a round pistol grip, a stock cutout below the bolthandle and a "Schnabel"-foreend tip. IMHO it is a typical post WW1 sporterized Karabiner 98AZ. Commercial Mauser C-type (army-hunting) rifles usually featured a bigger triggerguard, a shorter tangent sight and no cutout under the bolthandle.

BTW, when I was a boy of about 10, my grandfather took me to a relative's hunting party to learn the job of a beater. There also was a very old gentleman, much respected and addressed as "Herr General" by everyone. Only later I learned this was v. Lettow-Vorbeck. My uncle was Hauptmann/Captain Erich Müller, who fought WW1 in east Africa to the end November 14, 1918 near Abercorn. I was told later Erich Müller, as an avid hunter and fine shot, also did some sniping in the African bush. For the rest of his life he deeply regretted he shot a British officer who later turned out to have been the famous hunter he had respected so much… But a war was going on at that time…

OOPS, for British parlance I should not write "hunting party", as no horses, red coats and hounds were involved. It was a typical German drive for hare (a larger relative to rabbits living in the open, no burrows), a social event also.