Marco Langbroek, a space expert who tracks North Korea's missile program, told CNN he noticed something strange about the stars in images taken from opposite sides of the missile launch.
"You should see constellations that are opposites in the sky. That is not the case," he said.
Langbroek determined the direction of the photos based on the shape of the plumes of smoke coming from the rocket engine.
In the early hours of Wednesday, North Korea test-fired what is believed to be its most technologically advanced long-range ballistic missile. North Korea state media reported the Hwasong-15
reached an altitude of 4,475 kilometers (2,800 miles), putting the "whole" US mainland in range.
Langbroek, who is based in the Dutch city of Leiden, said he's been studying the photos since they were released by North Korean state media last week.
Something was off; to shoot stars, photographers use a longer exposure to more let light in. However, the longer exposure means that movement is captured as a blur.
When photographing a missile at night, photographers would use a wide-open aperture and fast shutter speed to capture the missile's rapid ascent. Stars wouldn't show up that clearly in an image, even in North Korea, where there's very low light pollution.
"They looked so crisp, that just didn't seem right to me," said Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics who corresponds with Langbroek.
Not all the images appear to be tampered with, Langbroek said.
One shot of the Hwasong-15 erected before launch shows the stars in the background, but also shows blurry individuals in the bottom-right corner, a sign that a long exposure was used to capture the night sky.
Ears to hovercrafts
North Korea has a reputation of altering images it releases to the world, tampering with everything from Kim Jong Un
's ears to hovercrafts conducting an amphibious landing.
The concern with aesthetics could explain why North Korea may have tampered with its missile photos. The starry background helps highlight the missile and give it an ethereal quality, giving the photograph some texture that a near pitch-black background would not.
But the enhancements could also throw off those who study North Korea's missile program.
North Korea has conducted most of this year's missiles tests during daylight hours, and background landmarks help analysts locate exactly where a missile was launched.
That's an important data point that helps experts calculate everything from range to payload.
Using stars to locate where a missile was launched is much more difficult.
"Stars just don't look that different a few miles apart, and we have no reason to disbelieve that this launch was from the Pyongsong region north of Pyongyang," McDowell said.
By conducting the launch at night and altering backgrounds, it's possible that Pyongyang was trying to throw everyone off.
Jeffrey Lewis, a nuclear weapons expert at the James Martin Center for Nonproliferation Studies, said on his latest podcast his team will use forensic software to lighten the nighttime images for clues. When asked about Langbroek's findings, Lewis told CNN they are still running the images.
But McDowell believes the images were only edited for aesthetics because the missile itself does not appear to have been altered.
"I don't think we've seen any evidence of that, so it looks like they just cut out a star background and put it on to make it look cool," he said.