Did some more digging...looks like I was partially correct. The first Pershings in country were the Marines' and the Marines never had the M45. However, at some point during the Pusan fighting the Army's Pershings started to arrive. That photo is one of the tanks from the Army's 6th Medium Tank Bn.

I found it with a label in two books, both by Steve Zaloga: "T-34-85 vs Pershing: Korea 1950" and "M26/M46 Pershing Tank: 1943-1953"

Those books have some other angles for photos, too, that should be helpful.