The helmet depicted in picture 1, is not in my professional opinion a US flight helmet or high altitude helmet. I base this on 24 years of experience maintaining/inspecting/repairing/building USAF flight helmets. The "Bib" as pointed out by DCMatt is counterproductive of flight helmet designs and that is allowing as much movement as possible. What most people don't know is that flight helmets while affording some measure of protection, was designed as merely a suspension assembly for the communication systems, and oxygen mask.
The helmet depicted in picture 2, has the appearance of Soviet styled high altitude helmets.
As for space helmets, one must remember that they lock on to the suit. There-fore they have a locking ring/seal at the bottom, the helmet is rotated to lock/seal on to the suit.
The reason for the two different helmet remarks, is that your first picture it shows a dark flip down visor, the second picture shows no dark visor and no provision for attaching the visor. Leading to some confusion as to whether it's the same helmet or two different helmets.
Pictures 1 and 2 below show my Chinese TK-1 high attitude helmet (Chinese copy of the Soviet GSH-1 helmet) with the visor attachment assembly. This helmet is dated 1972.
The picture below shows my HGU-26/P helmet with the hard visor assembly. Helmet in use from the 60's until the early 90's.
Picture below shows my HGU-55/P helmet with the light weight visor assembly, that just snaps to the helmet. Helmet in use from the 80's to present.
