Not having seen the service record, I can't comment on what it might reveal. For that reason, I'm in no position to disagree about when Duckworth received his commission. I will take a look at records of the company officers to see who held rank at the end of the Atlanta Campaign.
Here's my contention -- at this late stage of the war, very few men in the Confederacy had the experience, supplies and equipment to make photographic images, probably fewer than ten. The nearest city where Duckworth might have located someone who could take his image would be Mobile, Montgomery, or Columbus, Ga. And that's no sure bet.
For that reason alone, I don't believe any Confederate images were made at Florence.