The new director of the National Portrait Gallery, which holds the competition every year, has only just taken up his post, after 11 years living in the United States, and arrived long after the selection and judging process for the prize took place. Presented with the 45 finalists, he was struck by the bleak, confronting, sinister, uncheery atmosphere they create when taken together.

A war amputee, a man contemplating an open oven in a dingy room, a pair of kids with chicken pox, a middle-aged heroin-addicted prostitute shooting up in a car, twin asylum seekers living in limbo, an exhausted miner in a filthy kitchen - life in all its glorious, uncompromising diversity is on show here. On a bad day, that is. If this show were taken, as it is intended, as a snapshot of the Australian psyche represented through photography, then life is hard.

But this, Trumble says, is baffling when he considers how buoyant Australia feels to a prodigal son like him.

"For me, it's very interesting coming back to Australia from many years abroad. I'm struck by the darkness of mood, which is unquestionable, but compared with a brightness of general atmosphere in the country," he says.

"I'm not talking literally, I mean figuratively. Australia is very buoyant at the moment. I mean, we're a grumbling sort of nation, we like to grumble - about the motor industry, about Qantas, the governing classes and bureaucracy and everything. But honestly, compared with the United States, things are pretty good! Over there, there's widespread poverty, widespread homelessness. It's a very glum atmosphere."

This year's prize selection need not be cause for despair, lacking in levity - or even smiles - as it is. "I think the dark is not necessarily sinister - the dark can be cool and shady and reflective, or pensive, and poetic," he says.

But how to pick a winner? The prize is open to anyone over the age of 18, both amateur and professional, and the winner takes home $25,000. A win can be both a career-defining moment or another trophy for the mantelpiece; last year's winner, 22-year-old TAFE graduate Janelle Low, was weeks away from heading to Centrelink when she got the call. In 2010, a Perth high-school teacher won for a spontaneous snap of a student, while the winners in 2011 and 2012 were both established photographers who had carefully crafted their winning images.

The exhibition is accompanied by onscreen interviews with the judges talking about the selection process, as well as a peek at the process taking place. But, ultimately, the process is as simple and fair as possible. The three judges trawl through hundreds of entries - there were about 1400 this year - scrolling through them on a computer screen. At this stage, there is no background information on either the photographer or the sitter. As each image flashes up, the judges sort them out, based on their reactions, or lack thereof. Those that leave all three nonplussed invariably get the flick. It's only later that the images begin to take shape with their background stories and information about the artists.

While the winning image is chosen unanimously, the decision is never reached without a good deal of disagreement and healthy debate. Historian and curator Sarah Engledow, one of this year's judges, says the 2014 winner was the clear choice of fellow judge Greg Weight, himself a professional photographer. The simplicity of Andrew Cowen's stark, thoughtful portrait of the cartoonist Matthew Martin belies the complexity of the process of creating it.

"The sparseness of this image looks easy, but is actually very, very difficult to achieve, an image of this degree of elegance, this sharpness," Engledow says.

"He's both looking in and looking out. The eyes are just amazing, and it is true, he could be looking at the most tragic thing he's ever seen - he could be watching his mother dying or he could be just looking at the corner of the room."

She says the image is undeniably stunning, but not one that caught her eye from the outset. This year's runner-up - a gritty self-portrait by Melbourne artist David Apostol - is the one she found herself returning to again and again.

"There's a real Coen brothers menace and indeterminacy of it all … the composition of the work and the colouration is just beautiful, the grime is just spectacular," she says.

"He's just got the coolest and most uncompromising look - you just don't know which way he's going to go, you don't know what kind of guy he is, you don't know what's going on here. Why is the oven open? He's got a rollie in his mouth and … what's he got in his hand? He looks like he could be about to blow up a hostage. It is nihilistic, and yet it's playful because he does have that [remote control] in his hand and it is a self-portrait. It's quite manipulative."

She's also taken by the fact that Apostol is, by day, a tram driver in Melbourne, while Cowen is a professional photographer.

Another image that captivates her is a portrait by Andrew Tsangarides of a young woman, Fatima, from Cabramatta. "Every time I look at her I wonder where she's heading. I just find this such an astounding face and presence."

There is, as she points out, nary a tooth to be seen among the 45-odd faces on display, and only a hint, here and there, of a wry smile, and one of those is on the heroin addict in the car. Engledow puts the lack of smiles down to the photographers making a concerted effort to reveal some sort of essence of the sitter. After all, not many smiling faces can be seen in the great tradition of the portrait over the past few hundred years. Smiling uses a lot of muscles, so painters avoided it in favour of sombre expressions or upturned mouths with nothing showing in the eyes (eg Mona Lisa). Later, early photography required such long exposure times that it was much easier for sitters to remain expressionless during the drawn-out process of a photograph being taken.

"No matter what cameras can do now, our idea of a profound portrait is caught in the twin strands of this tradition of gravitas," she writes in an essay in the show's catalogue.

Just don't check out the show if you're feeling down.

The National Photographic Portrait Prize 2014 is at the National Portrait Gallery until June 9, alongside PROMO: Portraits from Prime Time. Entry for the two shows is $10, or $8 for members and concession. Under 18s are free.