Pattern-recognise the calcification first.
On a KUB film, the diagnosis usually comes from the SHAPE and SITE of the calcium. Here there is not one stone but a SCATTER of coarse flecks laid out transversely across the upper abdomen. A band of multiple small calcifications running side-to-side across the epigastrium maps onto one organ - the pancreas, which itself lies transversely at the L1-L2 level.
Why pancreatic calcification looks like this.
In chronic pancreatitis, repeated inflammation precipitates protein plugs inside the pancreatic ductules; these plugs mineralise into calcium carbonate stones. Because they sit throughout the duct system of a transversely oriented gland, the plain film shows multiple speckled calcifications strung across the upper abdomen - the hallmark of chronic calcific (often alcoholic or tropical) pancreatitis.
Knock out the alternatives by location/number.
$\bullet$ Enterolith: a solitary rounded calcified mass inside a bowel loop, not a transverse scatter.
$\bullet$ Calcified mediastinal nodes: these are in the chest, above the diaphragm - they have no business on an abdomen film.
$\bullet$ Horseshoe kidney with stones: calcifications would track to the renal beds/paraspinal gutters low across the midline, following fused lower poles, not the pancreatic line.
So the radiograph is diagnostic of chronic calcific pancreatitis (D).