Washington, Dec 5 (IANS): The photographs North Korean state media released of last week's Hwasong-15 missile test appear to have been tampered with, an analyst said on Tuesday.

Marco Langbroek, a space expert who tracks North Korea's missile programme, told CNN that 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 November 28, North Korea test-fired what is believed to be its most technologically advanced long-range ballistic missile.

State media reported that the Hwasong-15 reached an altitude of 4,475 km, putting the "whole" US mainland in range.

Langbroek, who is based in the Dutch city of Leiden, told CNN that he has been studying the photos since they were released last week.

"Something was off; to shoot stars, photographers use a longer exposure to let more 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 would not show up that clearly in an image, even in North Korea, where there is 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.

However, 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.