How NYT verified that the video of Iranian missile hitting the plane was genuine and not fake?
Basically,
They collected the video from a WhatsApp group of the residents in that town where the plane went down.
Matched the buildings with satellite images of that location [read google earth/map] and pinpointed the exact ally.
From there the direction the plane was videoed to be travelling matched with the predicted path.
Flash and explosion sound difference matched with planes altitude. Proving it wasn't fake.
And also talked with the video poster and re-confirmed it.
Link in comment.
By the way, that video taker has been detained by Iranian government for taking and posting that video.