If there is one iconic jet airliner, it is the Boeing 747 with its partial upper deck. The "hump" comes in different lengths, but not along the whole fuselage, and this is what makes it different from the similar sized Airbus A380. Whilte that is normally enough to recognise a Boeing 747, also typical for the type is its main landing gear: four legs with four wheels, with the outer two bogeys significantly tilted backward when the aircraft is in the air. Other typical features are the double landing lights in the wing roots and the APU exhaust in the middle of the roudned tail cone.
How to recognise the different versions of the Boeing 747 will be added later.
Confusion possible with
There is just one other jet airliner with a double deck and that is the Airbus A380. The latter has two decks along the whole length of the fuselage, the Boeing 747 only partially.