Commons does not require reliable sources or any independent evidence that an image or other file contains what it purports to contain. The author's or uploader's claims are normally accepted unless there is reason to doubt them.
Images and other files that are "known wrong", such as maps with outdated or disputed borders, may still be acceptable within theCommons:Project scope.
That said, if there is a reason to doubt the description, then contributors can attempt to update the description, or, in some cases (such as an unlabeled photomontage that amounts to a hoax), send the file toCommons:Deletion requests.