Finalists in one of photojournalism's most prestigious awards competition came away with far more than pictures while covering the fight for Iraq's Mosul, the longest urban battle since Stalingrad.

"In all my life as a reporter, I've never had suicide bombers right in front of me," said Patrick Chauvel, one of four finalists for the top prize at the Visa pour l'Image festival in the southern French city of Perpignan.

Chauvel, who has covered numerous conflicts since Vietnam, told AFP Iraqi soldiers and civilians were faced with "an army of suicide bombers" from Islamic State (IS).

"None of them had any intention of surviving. Obviously, that changes things."

This year was the first that all the finalists at the annual international photojournalism festival covered the same event.

The nearly nine-month battle which ended in July ravaged Mosul and took a heavy toll on residents and security forces. More than a million people were estimated to have fled the fighting.

"Everything was booby-trapped. There were improvised mines and mines everywhere. That complicated things," said Chauvel, whose work appeared in the French weekly magazine VSD.

And in the middle of all that, "a million civilians were stuck and used as human shields," he said.

- 'We were a target' -

By using snipers, mines and car bombs "ISIS did not conduct a conventional war," said Italian photojournalist Emanuele Satolli, another one of the four finalists.

"So the danger was everywhere. As a journalist, we were a target."

"The difficulty for me was to be close to the reality, where the civilians were leaving" their homes, said Satolli, who covered the battle for Time magazine.

The top prize, the Visa d'Or News, was taken home by Laurent Van der Stockt of French daily Le Monde, with organisers recognising that his proximity to the fighting -- he was embedded with Iraqi special forces -- gave his coverage a singular force.

To be as close as possible to the frontline, journalists can be "embedded" -- attached to military units -- with Van der Stockt operating alongside an elite unit that was under the direct authority of the Iraqi prime minister.

The Belgian photojournalist with around a quarter century of experience covering conflicts managed to cover the entire battle thanks to the relationship he developed with a commander who headed up numerous operations.

- 'Cost me dearly' -

"I never had such access to military operations and for that long," said Van der Stockt.

"Never or very, very rarely has a journalist gone with a small group of special forces.

"Usually they are with the advancing troops but never with the small groups making the penetration," he said.

Of the 450 journalists accredited to cover the fight, few were able to cross checkpoints and reach the front lines.

For Goran Tomasevic, a Serbian photojournalist who has covered wars in the Balkans and the Middle East for 20 years, "it is always a challenge to spend time" with soldiers.

"Once, they allowed me to stay full time with them for 10 days, following them for every mission," said Tomasevic, also a finalist who works for Reuters news agency.

- A shared moment -

At such moments, "there is a form of shared experience, where one ends up sleeping in the same ruined homes, taking the same risks," said Van der Stockt.

"Of course a rapport is established, and of course a journalist should try to remain as objective as possible."

But he said journalists had little other choice, as no independent reporters could work in the areas under Islamic State control.

"We knew it would be long, but not that long. Nine months, I had no clue," said Alvaro Canovas, who covered Mosul for Paris-Match magazine.

"Psychologically and morally, I didn't think it would be so hard. But it cost me dearly. With family and on all levels," he said.

Canovas now is planning to take a break from covering conflict for a while.

"There will be a before and after Mosul. Especially as that cost the lives of people dear to me: Veronique Robert, Bakhtiyar Haddad, Stephan Villeneuve," he said referring to three fellow journalists killed in a landmine blast in the city in June.

"That scars you," he said.