A haunting image of migrants passing a baby underneath a razor-wire fence on the Serbian-Hungarian border won the prestigious World Press Photo award for 2015 on Thursday - even though it had never been published.

Australian freelance photographer Warren Richardson made the moonlit image on Aug 28 and said he offered it to two news organizations, neither of which responded.

Jury members, however, saw something special in the black-and-white image. Vaughn Wallace, deputy photo editor for Al Jazeera America, said the image is "incredibly powerful visually, but it's also very nuanced".

The photo, he said, "causes you to stop and consider the man's face, consider the child. You see the sharpness of the barbed wire and the hands reaching out from the darkness".

Richardson said he did not carry any equipment to transmit his images while he spent days camping near the Hungarian border crossing at Roszke to document the passage of the migrants fleeing conflict, poverty and persecution in the Middle East and Africa. He said the delay in sending out his images from his home in Budapest may have been to blame for the lack of interest.

It was so dark when he took the picture that Richardson did not even realize the migrants were passing a baby under the fence until he looked at the image on his computer. He checked the photos only once he got home to preserve his camera's battery.

"Had I used a flash, I would have given their position away to the Hungarian police," Richardson said.

The image won top prize in the contest, which drew 82,951 images from 5,775 photographers. It also won the Spot News Singles category.

Last year's competition was overshadowed by the disqualification of a winner who admitted that one in a series of pictures about the Belgian city of Charleroi was actually taken in Brussels, and by controversy surrounding the pictures of the gritty, postindustrial Charleroi.

Lars Boering, managing director of the World Press Photo Foundation, said the contest set up a new code of ethics for this year's contest to ensure the integrity of images. He praised photographers for largely sticking to it, saying there were more checks and "fewer problems" than last year.