A subjective answer is, if you have been there and know this to be real from personal experience.
A more general answer would be, as long as we humans sufficiently interact with reality, we will have a respository of life experience to benchmark against.
Once we cease to do that, and are the product of a life in front of the screen, then we won’t know anymore.
Edit: This place is relatively close to where I live.
The very same question like it is, could be literally repeated under any article and is definitely offtopic as it is a general debate how to spot AI and what are the limits of knowledge. Interesting offtopic, so tolerated here if the debate that follows is interesting, but offtopic nevertheless. More ontopic would have been to state why these concrete pictures seem fake.
We only know now because generated things still have artifacts. That is slowly changing. If the article was written by an AI right now absolutely cannot be fully known.