The photo was hanging on a wall in the background as state TV showed footage from an arms and munitions industry conference attended by current dictator Kim Jong-un.
It shows the new leader’s father, who died in 2011, looking at a large globe-like object with other officials from the regime.
North Korea observers believe the object could be an atomic bomb, pointing to similarities between that image and recent snaps showing Kim Jong-un inspecting what Pyongyang claimed was a hydrogen bomb, one of which was hanging nearby.
The photo of Kim Jong-il and the round object was first spotted by a China-based Twitter user, the BBC reported.
The user, xutianran, wrote: “Is this an A-bomb or sth [something]?”
That sparked an effort to try to verify the object, with speculation that it could have been taken in 2006 or 2009 when Kim Jong-il oversaw nuclear tests.
But it is still possible that the globe is a mock device given its small size, the report added.
The hermit state has inadvertently given away some of its secrets in past state news reports.
In August, new ballistic missile types were seen on wall charts as Kim Jong-un visited a defence facility.
North Korea has carried out a series of intercontinental ballistic missile tests this year, in addition to its sixth nuclear test ever, despite UN sanctions.
Pyongyang is working to develop a nuclear warhead capable of reaching the US mainland, and the dictator recently told of his plans to include atomic bombs in its arsenal of catastrophic weapons.
He vowed to make North Korea the world’s “strongest nuclear power” as he spoke to military scientists this week.
The despot said: “We will develop new strategic weapon systems, including atomic bombs, hydrogen and intercontinental ballistic missiles.
“Our defense industry, self-defense power has been enormously strengthened at an extraordinary speed, and our republic will become the world’s strongest nuclear power and a military power. We will fight for it.” (Mirror)