By Jonathan Amos Science reporter, BBC News

The picture was very nearly deleted from the camera Enlarge Image

A picture that took nine years to obtain and was almost deleted at the last minute has won the Shell Wildlife Photographer of the Year award.

Goran Ehlme's shot of a walrus feeding on clams on the sea floor is a whirl of grey; the animal's face is seen poking through a cloud of disturbed sediment.

He caught the magic moment on a digital camera and deleted many unwanted shots.

"My finger was poised to delete this one too, and then I noticed something special," he told the BBC News website.

The competition has become one of the most prestigious in world photography.

It is organised by BBC Wildlife Magazine and London's Natural History Museum. This year brought more than 18,000 entries from 55 countries.

Goran is a highly experienced natural history filmmaker. His work has featured in the BBC's Blue Planet and Planet Earth series, and on National Geographic TV.

The Swede has spent almost a decade getting to know the behaviour of the walrus and how to get close to the mammal without being attacked.

You get a real sense that you're seeing something you've never seen before. Epic Andy Mclane, competition judge

Weighing 1.5 tonnes, these beasts can be extremely dangerous if they feel threatened, and their big tusks have been known to kill even the great Arctic predator, the polar bear.

"It was while the walrus had gone to the surface for air. Underwater, with a mask on, with a housing around the camera, it was really hard to see the little screen; but I suddenly thought 'wow!, there's his head in the cloud'.

"It looked really great."

The judges certainly thought the image was very powerful.

"It's got everything, the feel of the picture is interesting, your attention goes straight to the eye. A very simple graphic image showing interesting behaviour," said chairman of the judges, Mark Carwardine.

Judge Andy Mclane added: "You get a real sense that you're seeing something you've never seen before. Epic. You could spend years trying to get this shot."

This year's prize for Young Wildlife Photographer of the Year has been won by 17-year-old Rick Stanley from the US.

On this occasion, the frog did not become a meal Enlarge Image

Taken during an expedition in the Dominican Republic, it shows a distressed Hispaniolan treefrog in the grip of a green vine snake.

"I photographed the drama as the frog dangled in front of me, but [my friend] Rubio was unable to resist helping the victim and gently touched the snake, which promptly dropped its meal and slithered away along the branches."

The frog, seemingly unaffected by the snake's mild venom, hopped off.

Rick has called the picture The Dilemma because the incident left him wondering whether it would have been morally better to let the snake have its meal - and if it would have succeeded in swallowing such a large frog had it been left to try.

A picture that is sure to grab a lot of attention this year is Todd Gustafson's photo of flamingos at Lake Nakuru, Kenya. It can be seen on publicity posters for the competition's exhibition at London's Natural History Museum.

Pink and puffed up Enlarge Image

It is a scene Todd knows well having grown up in that part of Africa. The lake becomes a mass of pink as the birds gather to find a mate.

This "stand" of male birds is pictured at the edge of the courtship dance floor, their puffed up postures ready to impress the females.

"It totally captures that moment, and totally captures what those birds are all about," Todd told the BBC.

"These guys are just amazing. The best thing for me is the angle of view. I'm not looking down on them; I'm lying on the lake bed, looking straight at them; so behind them is all pink."

Todd's image was a runner-up in the Animal Behaviour: Birds section.

Igor Shpilenok's shot of a bear peeking through a window wins the Urban and Garden Wildlife section.

The picture was taken at Igor's cabin on the Kamchatka Peninsula in the Russian Far East.

A one-shot wonder Enlarge Image

He heard a noise in his porch. "Thinking it was my colleague who lived next door, I invited her in, saying the door was open," said Igor.

Receiving no response, he got up and pushed the door open with his foot. When the door bumped against something, Igor stuck his head through to apologise. It wasn't a person but a bear, which had prised open the outside door and was having a good nose around.

"It looked up at me in a seemingly friendly manner, but nevertheless, I quickly closed the door," said Igor.

He grabbed his camera to take this one and only picture. A lemon left to ripen on the sill adds a nice twist to this still life.

You have to have the right tools to crack open a coconut, and this fella certainly has them.

The frame is everything Enlarge Image

The coconut crab is possibly the biggest arthropod on land, with a leg-tip-to-leg-tip length of up to one metre.

It also has extremely strong pincers.

Jan Vermeer's picture was taken on Aldabra, in the Indian Ocean.

"The composition works well in this picture," Jan said. "As the crab walked up, I saw the other trees on both sides. I put the animal in the middle, and that way you put him in his behaviour; you are able to tell a story."

The image was the winner in the Animals in Their Environment section.

An exhibition of the best images from this year's competition opens to visitors of the Natural History Museum on Saturday 21 October 2006 and runs until 29 April 2007. It will then tour across the UK and five continents after its London debut.

Jonathan.Amos-INTERNET@bbc.co.uk