Fairfax photographer Joe Armao spent an entire night studying the strange, hair-raising blur on one of his pictures before reaching the conclusion it was the result of a highly unusual combination of the Gallipoli dusk, a tiny movement of his camera, the 2.5-second exposure period and a weird dark space on the frame created by a gravestone flower in the close foreground.

Armao was astounded when one frame of a series of pictures he took Tuesday evening at Beach Cemetery beneath the old Anzac battlefields revealed what appeared to be the shape of a figure in a broad-brimmed hat lurking in the gloom.

In 25 years of photography,he had seen nothing like it in any of the hundreds of thousands of frames he had captured.

Only three people were at the cemetery, or anywhere, so far as we were aware, within kilometres: Armao, guide and local author Celal Boz, and me.

Celal was standing among the silent graves, the only person - no more than a silhouette - in the camera's field of vision.

By the time the shutter closed, what appeared to be another spectral figure had been captured by the camera: the shadowy silhouette of a figure in a wide-brimmed hat appeared in the frame.

In the foreground is a flower that grows between the gravestones. The extra silhouette appeared in only one frame of three near-identical pictures taken over 40 seconds. The camera angle had changed no more than 15 centimetres over the series, and the shutter had been set for a 2.5-second exposure because of the gathering dark.

Hours of close and sceptical inspection of the frame, including extreme digital enlargement, comparison with other frames and lively discussion of a number of theories about shadows from the flower, tricks of the light and movement of the camera during the 2.5-second exposure offered no suitable explanation.

But Armao, no believer in the paranormal, could not rest and spent the night studying and re-studying every possible angle. If his camera had moved during the exposure, how could it be that only one part of the image had blurred sufficiently to create the extra silhouette?

In such a case, the whole picture should have contained such shadows. But while other flowers had cast small and near-perfect silhouettes into the darkness, how could just one melt into what appeared to be an apparition of precisely the same height and dimensions as the man actually standing in the cemetery?

A minute study of the pixels finally revealed the mystery. Because the little flower in the extreme foreground was so close to the lens, the tiniest movement had created a large space of nothingness - the largest on the frame - which had imprinted itself on the image as "something" - in this case, a shape resembling a soldier rising from amid the graves.

The dusk at Gallipoli can exercise the imagination, but it can also trick the lens of a sophisticated camera.

It was simply an unnerving moment in a darkening graveyard, 99 years since Anzac soldiers stormed ashore at nearby Anzac Cove, captured between the opening and closing of a shutter.