[David]

All armies in WW1 were initially taken somewhat aback by the potency shown by the aerial forces, and in most cases means to counter this new threat from above had to be improvised. There were real AA guns for sure, but these were too few for the demand, and all armies experimented with using regular guns in improvised new mounts or different contraptions, more or less strange, enabling these pieces to fire at flying targets.
This gun is such an improvisation, made by the French, and obviously not an alltogether failed one at that.
The gun is a standard 75mm mle1897, but it has been mated to the carriage of a mle1882 (less the 120mm gun, of course) allowing for a much higher elevation. The gun was also put on special platform, allowing the whole gun to be quickly traversed as well - therefore the big handwheel to the left of the breech. This particular gun has been captured by the Germans, and used by them - hence the German type camouflage.