FeldzugImOsten105

This appears to be a Pak38 and almost certainly a posed propaganda image from the Eastern Front

While the 37mm PaK 35/36 anti-tank cannon proved a success during its trial in the Spanish Civil War, German authorities knew that the system would quickly become outmoded by heavier armoured tank systems (some already in service at the time). Rheinmetall of Germany began work on a towed 50mm (2-inch; 5-cm) caliber version in 1935 with the designation of PaK 37. However, German authorities were not satisfied with the weapon's low-velocity action, forcing Rheinmetall to rework their product. The company fitted a new, longer L/60 barrel and returned with the PaK 38 to which the Germany Army accepted for production. Production began in 1939 and examples reached German troops in 1940, though this was too late to take part in the German campaigns across the West Front. Once in service, the PaK 38 operated as part of dedicated anti-tank platoons though it would not be until 1941 that the anti-tank gun would see its first combat actions - this as part of the German invasion of the Soviet Union through "Operation Barbarossa".
https://www.militaryfactory.com/armor/detail.asp?armor_id=349