But they are shown a painting which is pretty obviously just whatever the person creating it wanted it to be, nobody would ever accept it as a perfect record of reality. I don't understand how photography comes into things?
* captain arrives in FTL ship looking for evidence of a thing
* captain isn't satisfied with a painting offered as evidence, because it could be fake
* aide says that photography is unknown to the natives, implying that the production of a photograph would be taken by the captain as having more evidentiary value
=> captain knows about FTL but is unfamiliar with the technology required to produce false but convincing photographic images