The submarine anchored at Sinpo shipyard on the country's northeastern coast has a length of approximately 67 metres and a beam of 6.6 metres, according to the website 38north.org associated with Johns Hopkins University which published the photographs taken July 24.
Experts do not know the exact origin of the submarine which bears similarities to Russian and former Yugoslavian submarines.
38north.org analysts predict that if the submarine design is successful and begins to be produced in series, the vessel will be an improvement in range, autonomy and attack capability to those currently in service with the North Korean navy.
However, experts from the research institute recognise that "it is possible that it is an experimental model manufactured to check certain parameters of design and equipment", as the North Koreans have done in the past.
Because of its design, it does not appear to be a prototype of submarines that launch ballistic missiles.
The South Korean army reported recently that North Korea was developing a system to launch ballistic missiles from modified Golf-class submarines.
Sinpo shipyard is the largest submarine factory in North Korea and is also the headquarters of the Maritime Research Institute of the Academy of the National Defence Science, responsible for the research and development of warships and submarines, as well as armament and naval missiles.