Pitting amateur against professional on an entirely level playing field is a rare thing in any strata of life, not least the world of photography.

And yet that has long been the arena of the (UK) National Gallery's Photographic Portrait Prize, which has for some years been sponsored by Taylor Wessing.

"It is an open call for anyone who is practising photography within the genre of portraiture," says the Scottish National Portrait Gallery's International Photography Curator Annie Lyden, who welcomes the return of the annual prize to the Gallery after an absence of 17 years.

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Submissions, which this year ­numbered more than 5000, are blind and so judges may have little idea whether they are looking at the work of a dedicated amateur from Southend or an internationally recognised photographer from Sao Paolo. "The judges are basing their decision purely on the photographic print," says Lyden.

This year, the overall £12,000 prize was won by a professional photographer, Spencer Murphy, for his striking portrait of jump jockey Katie Walsh, who was third in the Grand National in 2012 on Seabass. But the fourth prize was won by Dorothee Deiss, a paediatric endocrinologist from Berlin, whose rather joyous image of two elderly twins lounging on a day bed repaid her passion in her hobby.

"That is the great thing about the Prize," says Lyden. "No one knows who the images are by." It also means that, on rare occasions, a photographer with particularly strong images may appear in the exhibition more than once, as has Rosie Hallam this year with her large-scale life-affirming portrait of an ebullient Ghanaian choirmaster and a portrait of the model Lily Cole taken at the Hay-on-Wye Literary Festival.

Lyden, who has put her own curatorial imprint on the selection in the rehang for the Edinburgh gallery, has been struck by the scale of many of the prints. In a world where images are often seen at the size of a smart phone screen, the physicality of the printed, framed image is striking. "It is an interesting time because with our phones and tablets, we see more visuals than ever before, and we have become more conversant in looking at photos. But the power of a show like this is that it you can see it up close and appreciate it in terms of the scale."

If many of the 60 portraits in the exhibition are large scale, every one tells a story, from Vincent Voignier and Barbara Bernardi's 'Botticelli-esque' Olivia, a dishevelled young woman photographed emerging from a Berlin club the morning after the night before, to Sipke Visser's Three Generations, a shot taken in a maternity ward of newborn, mother and grandmother, all asleep, exhausted.

There are serious issues lurking behind some of these images, from a grouping that loosely examines the idea of the portrayal of women - a portrait of a girl with her doppelganger American Doll is placed near an image of a young women in post-op recovery from extensive plastic surgery - to the preponderance of images relating to family.

There is humour too, not least in the eye-catching Fabio, a brightly coloured image of a cheerful, bearded man with a full-grown goat in his backpack, by Italian photographer Andy ­Massaccesi. Fabio himself, a resident of a small village in Switzerland, apparently used to smuggle goats across the Italian border. "This is a very funny image for me," says Lyden. "The goat looks at home in the backpack, as if this happens all the time. It might seem bizarre and surreal, but it is apparently quite within this man's normal practice."

There are famous faces, too, from a smiling Professor Mary Beard, photographed by Adrian Peacock after she had received appalling abuse about her appearance on social media, to Carl Court's unexpected and intriguing snap of Queen Elizabeth, taken while touring the Royal Academy Of Arts in London. Figures from the arts also appear, including Zadie Smith, photographed by Linda Brownlee gazing out of a window in a London tavern just before the publication of her recent novel, NW.

But one of Lyden's favourites is Martyn, Sean And Jacob, a portrait of three young men taken in Great Yarmouth by young photography graduate William Lakin. "I love this one in particular because these three guys are so interesting," says Lyden. "They almost do not seem like they would be friends, because each one is so stylistically different. I like the way Lakin has sort of caught them on the street…" she says. "They are staring at the photographer, almost sizing him up. There is a very interesting dynamic going on here."

That dynamic is something that the best of these images capture, whether the subject matter is teenage boys in a provincial English town or a young girl gazing dreamily out from a balcony in a factory town in the Dominican Republic.

The Taylor Wessing Photographic Portrait Prize, Scottish National Portrait Gallery, Edinburgh (www.nationalgalleries.org.uk, 0131 624 6200) until May 26, daily 10am-5pm (7pm on Thursdays)