Why does the UH-1 Huey have a hump at the rear of the cabin?
A copy of the original image can be found here, which is about 5 'pagedowns' down this page, which has a number of other excellent Huey-model photos.

It's a bit of structure to guide the rotor forces into the rest of the airframe, it would not be good if this bit went missing.

Fwd/aft, left/right, up/down. The rotor provides the lifting forces and driving forces and these are quite concentrated around the rotor axis. Picture the airframe like an empty beer can - some panels are required to cope with the forces while remaining in shape.