Aircraft series type designation
On another popular website featuring an extensive catalog of 'airliner' photos, the photos are usually accompanied by background information regarding the shot. One of the items is the aircraft type; 747-412, 747-45E, 737-844, 767-35E etc etc.
How does a spotter obtain such specific information regarding the aircraft he's shooting?
Also, what difference would one find between a 412, and a 45E anyways? Or aircraft of any other series for that matter?