Information on this photo is thin and conflicting. I’ve gone with Getty Images as the most trustworthy source. Some other dubious sources (reddit and Facebook) list the photo as either of a US Army soldier or of a US Marine with no citation. The uniform is a USMC M1942 utility uniform rather than the US Army in the pacific’s camouflaged one-piece utility suit, however given the mismash of uniform pieces seen going into the pacific, I find that not particularly persuasive of anything. If the photo was taken at Fort Belvoir, then it would point to a US Army soldier as that was a US Army training ground in WW2.
The flamethrower is the older M1. These would be replaced by M1A1s and then eventually the M2 family of flamethrowers, which the US would use until near the end of the 1970s.