On 14 October, the Frieze Art Fair opens its doors for its annual long weekend in Regent's Park in London. Showcasing 170 contemporary art galleries from all over the world, it's the biggest fair of its kind in the UK, and has grown to take up a pivotal place in the international art calendar since its launch in 2003, gaining particular reputation for its cutting edge.

Photography has an interesting place within it. Galleries that represent photography are welcome, but only if they represent work in other media too.

Galleries that represent photography and only photography, such as Michael Hoppen in London or Janet Borden in New York, are never given any space. So while Hiroshi Sugimoto and Andreas Gursky are in, because they are represented by Gagosian Gallery, the work of other key photographers will be conspicuous by their absence.

"Photography is an art form but we're looking at artists working in photography rather than photography per se," says Matthew Slotover, who together with Amanda Sharp, co-founded the art fair 12 years after setting up Frieze magazine with Tom Gidley. "It can be a difficult line to draw but people generally know what side they're on. Everyone understands that photography shown in art museums and galleries generally has a particular philosophy behind it."

As Slotover says, it can be a difficult line to draw. Wolfgang Tillmans' work, for example, will be at the fair because he's represented by contemporary art galleries around the world, including Maureen Paley in London.

In fact, he's even giving a talk at the show, alongside Ramin Bahrani, Susan Hiller, Amar Kanwar and three other artists using photographic images and film. But Tillmans started out as an editorial photographer on i-D magazine, and still works with magazines such as Fantastic Man and Butt, keeping one foot firmly in the world of photography.

Other photographers - Nigel Shafran, for example - have shown their work at Frieze when they were with a contemporary art gallery, only to disappear when they moved to a photography specialist, or go it alone.

"It is a blurry line - there are people who can quite happily show in an art gallery," says Slotover. "But the way Tillmans thinks is in keeping with other art photographers. I was on the Turner Prize jury when Wolfgang Tillmans won the prize [in 2000] and one judge did say they didn't think Tillmans' work was art because it was photography. The rest of us said, ‘Of course it's art and it should be recognised as such'. But that was 10 years ago - I don't think there would be any question about that now."

Slotover claims that he is "media blind" and doesn't distinguish between different forms of art, and points to Frieze as evidence. Rather than working with galleries that specialise in one particular media, he works with galleries that show interesting artists, he says, whatever the materials they use.

Photographers, he hints, might do well to take the same approach, rather than sticking to what amounts to a media ghetto. "When Gursky was offered a show in the photography department at MoMA [the Museum of Modern Art in New York] he said, ‘No, I'm an artist and I'll show in the art department'," he says. "It is interesting that there are separate photography galleries when there aren't specific sculpture or painting or video galleries. It's a funny one."

Of course you could argue that if Frieze really were media blind, it wouldn't distinguish between galleries that specialise in photography and galleries that don't, but that argument cuts little ice with Slotover, not least because Frieze is already so oversubscribed.

"This year is the biggest yet and if we were to accept more galleries, we would have to cut the space allotted to each one," he says. "We don't want to do that, and unfortunately we can't increase the space because we're based in a park and there are trees in the way." BJP