1. Wouldn’t viewers naturally trust more a photograph that has been manipulated to more perfectly depict the subject?

Not if they know (or suspect) that the photo has been doctored or aigmented, because that knowledge (or suspicion) will cause viewers to trust a photograph less (see #3 here).

2. Most people agree that all photos are “imperfect portrayals”

Building on that agreement, TTG is premised on the principle that — assuming that neither photo is misrepresentative—

viewers will trust an “imperfect portrayal” that is undoctored more than they will trust an “imperfect portrayal” that is doctored or aigmented.

(Again, see #3 here if the reasoning for this is unclear.)