That is certainly a dramatic picture, taken just after it has fired. But, it also look strange a) because of the raised promontory immediately behind the gun and b) the man to the left of the rear of the gun who appears to be buried to the waist. It could be that the image is actually two pictures fused together? It reminds me of the picture of the Boers firing on the armoured train (
I see exactly what you mean!
Certainly some commercial photographers did stitch photos together, or enhance them - I have seen several examples. Van Hoepen was a culprit of this practice, and he also notoriously posed or re-arranged some bodies on Spion Kop to make his picture. He also took several photos of Spion Kop twice, if I look closely can make out two similar versions of at least 4 famous photos taken by him.
This photo is, I think, legit: it's from an album of 142 photographs taken by an amateur photographer, Lt Loch, NAM Accession Number NAM. 1986-08-49-138
I think the Naval Gun is protected by being dug as a gun pit into a donga [dry river bed] - in this version I have outlined ground level in green, and there's a ramp down into the gun pit.
The past is not dead. In fact, it's not even past.