Crouching in the shelter of a knocked-out German 47mm anti-tank gun in Aachen, Germany, Pvt. William Zukerbrow, 1st Infantry Division, Brooklyn, N.Y., draws a bead on a Nazi sniper. October 29, 1944. (Signal Corps photo and original caption) [2048×1728]

Even an original caption can be wrong, this is a 2cm Flak 38 without barrel.
https://de.wikipedia.org/wiki/2-cm-Flak_38

The empty shell cases are most likely 7,5cm Pak 40 ones.
Every 2cm Flak carried at least one spare barrel and the actual one had to be changed to prevent overheating. So this one was either knocked out, or the crew removed the barrel so the flak couldn’t be used against them.