The Institute of Contemporary Arts may be situated slap bang in the centre of Establishment London, but don't expect to find anything conventional about its artistic programme. This cultural centre prides itself on being cutting-edge. It is a purveyor of postmodernism to the artloving public, and its latest show Dispersion - curated by Polly Staple, director of the trend-establishing Chisenhale Gallery in East London and former editor-at-large of Frieze art magazine - is no exception. Which means that if you want to find out what the exhibition is about, you can forget all the gallery's proffered publications on the show. From leaflets to catalogue, true to postmodern stereotype, they are mostly gobbledegook.

Dispersion is a group show of mostly film-based work by a selection of seven international artists that has no clear didactic message or easily traceable theme. The exhibition will also include a performance by the new Turner Prize winner, Mark Leckey, just before it closes next year. He will not be contributing anything as old-school as an object, of course. He will be delivering one of his stream-ofconsciousness style lectures.

What all the artists share is an interest in the notion of appropriation of images.As far as art history is concerned this is a familiar enough idea. From the early Christians who nicked pagan imagery, through the Renaissance artists who lifted straight from the Greeks to Picasso who begged, borrowed, pinched and incorporated from all over the place, appropriation is merely - as someone else said - stealing from thieves.

But where once the act of appropriation was something that an artist did to make a specific point, now, in our postmodern world, it has become the norm. The camera is ubiquitous in our lives.

This show launches you straight into its challenges. As you enter the gallery a piece of work by the German video artist Maria Eichhorn greets you. At first glimpse it might seem innocuous enough: just an old-fashioned film projector with a professional, white-gloved attendant beside it. What happens next is completely up to you.

Eichhorn invites the visitor to make their own selection from a dozen or so films on offer; if no one chooses anything nothing is shown. Mouth, apparently, is the most popular, and after that Eyes. It's easy to see why once you have read the complete playlist. The rest of the menu is dominated by Anal Coitus, Cunnilingus and Fellatio - each with a clear dictionary definition of what the term means alongside it (complete with etymological derivations), so you can't just pretend, when it comes on, that you didn't know.

The films show exactly what their titles suggest in very clear, full-colour and completely unflinching close-up. The deadpan scrutiny can be hard to take. Factor in a few fellow gallerygoers and you find yourself entering some fairly tricky territory. I felt an almost frantic sense of entrapment. Others, apparently, find it more comical

Meanwhile, the other artists stare into the endless stream of images - a bit like Zen masters are supposed to stare into rivers. They are always different and yet always the same.

Nothing is simple in this show. You see that sunset, and you probably feel all those nice feelings that come along with it. Well, it's not a “real” sunset, says Anne Collier. It hasn't been for an awfully long time - no, not even when you saw it last year on your Caribbean holiday. It was a highly-loaded image of a sunset even then. Collier shows an image of an image of that image to make her point.

And if you are looking to art for truth then forget it. Here is Henrik Olesen challenging the traditional categories of art history by re-examining its images not as canonical pieces or chronological events but as a document of gay culture. Hans Memling, Ingres and Corot, for instance, all come together for their lesbian gatherings of bathing lovelies, and a medieval Abbess Hilda holding out her breviary can suddenly find something in common with Gustave Caillebotte. In our cut-and-paste internet culture, Olesen says, you can collage together any number of images, customise them with your own interpretations and then disseminate them again at the click of a mouse.

Even your own rereadings can be reread, says Seth Price as he re-edits his own video works that were not ever really quite his: they were assemblages of other people's home movies and bits of documentary footage, advertising images and fragments of news.

In a piece that really makes this show worth visiting - wait and watch it from the beginning because the narrative is as important as it is riveting - the German-born Hito Steyerl sets out to recover a piece of pornographic footage that was taken of her in bondage when she was a student.

This film is a sinister journey into the world of S&M with a compulsive, punky soundtrack and (thankfully) a redemptive message. But, even though Steyerl eventually finds the original image, it turns out the more that you find out, that the girl trussed in the picture, isn't actually her at all. Truth can't simply be tied down, as this transgressive film suggests.

Art is certainly not going to offer an answer. Is it even art? Or is it just so much stuff, as Leckey, in his work, asks? It is questions such as these that make Dispersion worth seeing. Because even as they undercut all the prescribed meanings, they leave you more room to decide for yourself.

Dispersion opens today at the ICA, The Mall, London SW1 (www.ica.org.uk), and runs until Feb 1; Mark Leckey gives a live performance on Jan 31

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