I think that depends on the purpose.
- It’s a snapshot of a moment in time.
- It’s tool to tell a story.
(This idea also extends to videos, audio etc.)
As a snapshot of a moment in time, a photograph’s purpose is to capture as many details, as accurately as possible. It’s effectively converting light (photons) to pixels. Even though cameras with different sensors and lenses capture the same subject differently, in order to qualify for this category, it’s important that the photo not be modified once captured.
On the other hand, an artist may employ a variety of creative techniques to tell a story. In this context, a photograph is no longer an accurate representation of events, but a tool used by the artist to present their vision. Here, any amount of modification is acceptable.
Historically, it was possible to spot the difference between the two.