How do I know if a video is old footage recycled as breaking news?

I moderate a fairly big local news group. Every time something happens anywhere in the world, somebody posts "footage" within the hour, and nine times out of ten it turns out to be from a different event three years ago in a different country.

Right now I am going almost entirely on gut feeling, which is slow and sometimes wrong. What I want is a short set of checks I can run in two or three minutes before deciding whether to leave a post up.

What do you look at first? Weather, number plates, language on signs, something else entirely? I am more interested in what actually catches the most recycled clips than in the full textbook process, because I don't have time for the full process at 11 pm.