Scott Schuman’s window of opportunity has just blown shut. “That girl would have made a great picture! Right there!” He jabs his finger as our black cab executes a three-point turn in rush-hour Mayfair, and she’s lost for ever. “She was cute,” he sighs. “A little slinky, you know…”

As usual, Schuman is looking for people to photograph. It’s Fashion Week in London, but the girl disappearing in the rear-view mirror wasn’t a model or a celebrity. What she was wearing wasn’t even particularly on-trend. She was just a cool-looking girl looking cool in her own clothes. “The skirt was an interesting cut, lower in the back than the front… I love the fact she had that cardigan and a leather jacket. Her hat was good,” Schuman notes. “She was wearing it in a good way…”

Photographing ordinary people wearing clothes “in a good way” has made Schuman’s photo blog, The Sartorialist (thesartorialist.blogspot.com), required reading for the fashion industry and the three million people who visit the site every month alike. In an era when our traditional style icons (that’s to say, celebrities) are either photographed with their sweat patches circled on the covers of supermarket magazines or Photoshopped into unreality in billboard ad campaigns, Schuman celebrates the one group with enough intrigue and integrity left to fire our imaginations – real people. With his Canon G5 worn high around his neck, a hobby that started on the streets of his native New York now takes him all over the world.

“Scott’s pictures are compelling documents of the way today’s stylish people put themselves together,” says US Vogue’s European editor at large and fashion überauthority, Hamish Bowles. “These aren’t manufactured looks that have been contrived with the help of stylists; this is how his subjects actually dress themselves. That’s what makes them so intriguing and inspiring.”

Photos posted on The Sartorialist certainly invite enthusiastic feedback. “Wow! What a silhouette – and what a face!”, “I love how the French have turned looking amazing into a National Anthem”, and “Does anyone know where to buy those boots that tie up from the leg? I would love to buy them!!!!!!!!” run typical comments. Visitors also take it upon themselves to debate the finer points of a look; recent hot topics of conversation have included ideal summer plaids, inverted trouser pleats and the politics of wearing two jackets at once.

“People are looking to other people more than ever for their inspiration,” says Katie Baron, who, as bookings editor at Harper’s Bazaar, organises shoots with fashion’s finest photographers. “In economic uncertainty, there’s a necessity to get more creative to remain original. And if we’re turning back to basics for inspiration, people-watching is the most ideal source of inspiration there is.”

Unlike other fashion blogs, The Sartorialist comes to praise, not bury. “What I do is generous,” says Schuman, who is 41 and resembles Humphrey Bogart as redrawn by Pixar: all pumped-up chest and wobbly chiselled head atop his 5ft 5in frame. “I want to take a nice picture of someone, make them look good and put them on my site for people to look at. But it’s also very selfish. Because I don’t want to look at ugly pictures.”

After a day’s hunting Schuman might post up a single photo. Or none. And while he might be selective, he’s inclusive with it. Skaters, secretaries, schoolchildren, businessmen and workmen have all featured on the site. Some of The Sartorialist’s best shots are of immaculate pensioners. “I’ve had people say, ‘Oh, this is so silly, so frivolous, so unimportant to the world.’ But I totally think I’ve done something good. I’m proud of the fact that I’m one of the few fashion outlets where people can say, ‘Wow, that’s how I want to look when I get older.’”

Others clearly agree. Time magazine voted The Sartorialist one of its Top 100 Design Influencers, while Schuman had barely been snapping away for six months before Condé Nast recruited him to shoot for its influential Style.com website. A monthly page in American GQ, commissions from French Vogue and his own turn in front of the camera (as a star of Gap’s autumn/winter 2008 ad campaign) followed. A posh compilation book, also called The Sartorialist, will be published by Penguin in September, after Schuman rejected similar offers from publishers unable to meet his just-so requirements.

Meanwhile, the fashion world has itself been drawing inspiration from The Sartorialist’s street-style photography, taking sidewalk to catwalk. Dries Van Noten is a noted fan, as are the creative teams at Ralph Lauren and Paul Smith. “One time I went to this meeting at [US clothing brand] J. Crew and we were talking about khakis,” Schuman says. “I started to describe this picture [I’d taken], and the guy went, ‘Oh yeah, we know that picture.’ They already had a whole look based on that one photograph.”

You might argue what Schuman does is nothing new. And he’d probably agree. He is himself a fan of the Seeberger brothers, Parisian postcard photographers of the early 20th century who recorded society’s upper echelons in all their finery, and are now heralded as fashion photography forebears. And also Amy Arbus, who continues to record the New York life whose fringes so enthralled mother Diane. And readers of a certain vintage will recall i-D magazine going big on “straight-up” photography of club kids and street style in the Eighties. Yet Schuman is the first such photographer to make a name for himself in the internet age.

No shortage of similar blogs have followed in his wake – London’s Face Hunter, Garance Doré in Paris, Helsinki’s Hel Looks – though these tend to favour the trendy over the stylish. (Schuman’s own style is buttoned-down and classic; a well-cut cardigan, narrow A.P.C. jeans, French cuffs.) “Scott has an eye for the subtler characters whose looks tend to be based on a hybrid of styles,” notes Katie Baron. “It’s about finding those people who are a little outside fashion in terms of ‘trends’, who will shape the future landscape rather than reflect how it currently sits.”

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