I have flown in and out of JFK a couple of times, I remember at the T1 Terminal there is a little walkway to the side of the terminals where you can see the planes sitting at the T1 and T2 gates.
Then if you don't mind walking, you could go up to one of the parking garages, viewing is possible. I don't know about photographing. The last time I was over there was July 2000...back then some "rent a cops" came by and told me to leave, but honestly I did not bother....later on some guys from the NYC Port Authority came by as well, we chatted a little and then they left.
As for ATL.....you will be arriving at Terminal E (International Arrivals), you could do some viewing from inside.....not the greatest view but not that bad either!
No observation deck, although you could go to one of the parking decks!
For ATL, check with Ryan Gaddis, he is a local and I am sure he'll help you out!
For NYC, contact one of the NYC Boys, Joe Pries, Carlos Borda, Michael McLaughlin, they might be able to give you some tips as well!