Urban explorers: A new festival celebrating street photography illustrates how technology is blurring the genre

"What is the city but the people?" This observation from Shakespeare's Coriolanus is pithy enough, but it nonetheless belies the teeming flow of humanity in today's urban jungles. Indeed, visitors to the inaugural London Street Photography Festival may find themselves concluding that a picture is worth a thousand Bardic quotes. Running through July, the capital-wide event will celebrate the camera's unparalleled power to take the pulse – and herald the peculiarity – of everyday life, in the city and beyond.

But how to get a handle on this most slippery of genres? At the most literal level, street photography stretches back to the founding father of photography, Louis Daguerre, and his 1838 shot of the Boulevard du Temple in Paris. But it's more a question of attitude than pavement-bound subject matter: in the festival team's words, the key elements are that the picture is "un-posed, un-staged" and explores "contemporary society and the relationships between individuals and their surroundings". Happenstance, and the thrill of capturing the unexpected moment, also lie at the heart of the tradition which, since the invention of hand-held cameras in the late 19th century, has flourished in the hands of professional documentary titans (Henri Cartier Bresson, Diane Arbus) and sharp-eyed amateurs alike.

It's an amateur, in fact, who heads up the festival's archive strand: the startling photos of mid-century Chicago by nanny-turned-posthumous phenomenon Vivian Maier will receive their first UK showing. In the contemporary realm, meanwhile, it will provide a showcase for some of Britain's brightest stars, selections of whose work are displayed here. These include Polly Braden and David Campany with their collaborative project capturing the strange natural/industrial hybrid landscape of east and k north-east London's Lea Valley prior to its development as an Olympic site; Nick Turpin's ongoing series exploring his adopted French homeland; and Nils Jorgensen's portraits of English eccentricity.

From Braden and Campany's nostalgic poeticism to Jorgensen's boldly surreal compositions, street photography is evidently in rude and experimental health. The past year, especially, has been a boom time for the genre, with a Museum of London exhibition and a major survey book, Street Photography Now, on the subject. These are emblematic of the increasing visibility of street photography in the art world. "I definitely haven't seen a lot of street photography in galleries or an art context until recently," says festival programmer Grace Pattison. "Perhaps it was seen as less worthy or considered than other types of photography because its technique is so simple, but that's changing." Festival director Brett Jefferson Stott concurs: "I think a lot of institutions are now looking back at the archives and seeing its value as a record of society – of how people are and how they represent themselves."

Back on the ground, increased visibility has proved rather less desirable. In a recent interview, legendary New York practitioner Joel Meyerowitz spoke of our loss of photo- graphic "innocence": "Now when you raise your camera, everyone's eyes dart to you, because they're all fearful." Taking pictures of children in public places has been tainted by the spectre of paedophilia; meanwhile, countless British street photographers have found themselves challenged by police and private security guards, despite there being few legal restrictions on photography in public places. All in all, the kind of unmediated observation that is street photography's raison d'etre is under some threat.

The festival will address this with a debate entitled "Why does street photography make us paranoid?" Pattison, nevertheless, remains cautiously optimistic for the future. "With the amount of people who are behind freedom of expression, I can't see things getting worse than they are at the moment. In some countries they've prevented people from publishing street photography. I don't think it will come to that in the UK, although we need make sure it doesn't by encouraging people to talk about it."

But should we ever fear the prying camera and, if so, when? Paranoia, is, after all, understandable, in an age increasingly swamped by surveillance technology. It's a theme being tackled head on by a number of street photographers, including two in the festival: Mimi Mollica, with his images of bus passengers on CCTV screens, and Mishka Henner, whose "No Man's Land" projects plucks roadside images of women apparently soliciting for sex from Google Street View. Are these a comment on surveillance culture or complicit with it? Therein, of course, lies their ambiguous power.

By the same token, thanks to cameraphones and photo-sharing sites, we can all be the watchers now: you only have to glance at Flickr to see how street photography is thriving in the hands of the people. "The future of street photography is tied up with technology and the definition of it is continually changing," says Jefferson Stott. That we may only be a click away from discovering the next Vivian Maier is something to be truly snap-happy about.

The Independent on Sunday is media sponsor of the London Street Photography Festival, which runs throughout July: londonstreetphotographyfestival.org