faces to watch in the art world 3. Catherine Yass

Catherine Yass uses photography to scrutinise power and institutions. By interacting with her subjects she turns their smiles into cries for help, and their vanity becomes their downfall.

When the Arts Council Purchasing Panel wanted to buy one of Catherine Yass's works last year, the artist suggested making a group portrait of the panel itself. As a member of that panel, I was aghast when I saw myself in Yass's colour photograph, a shadow under my nose had been transformed into a blob of blue ectoplasm, while port-wine stains and psychedelic blips crept on to the rest of the panel's features. We had adopted our most winning looks for the shot, but Yass made us look alien, shimmering in the lurid aura of our vainglorious postures.

Yass's work is invariably related to the institutions in which it is shown, and to those who have commissioned or selected the shows. Her subjects have been the captains of industry, patrons, dealers, curators and critics, boardrooms, mental patients and eery hospital corridors. Her photographs, superimposing both positive images and colour negatives, are presented like illuminated ads, in light boxes. With their flourescent shadows, flares of light and peculiar contrasts, they have a hallucinatory feel.

Selected for the British Art Show later this year, she is currently in "Care and Control", an exhibition of installations sited in the derelict wards and treatment rooms of Hackney Hospital. For this show, Yass has made a poignant portrait of the hospital's drained hydrotherapy pool and has taken a spooky video journey through the tunnels of the decrepit basements. In another video, she tells a series of duff gags - doctor-doctor jokes, Jewish jokes and sick one-liners - to camera. It's not the way she tells them that make this an apposite work (her delivery is dreadful), it's the fact that she chooses to disrupt the sobriety of the setting with her morbid, mordant humour.

At 32, Yass has made a career out of the scrutiny of power and institutions, and her work frequently plays on the motivations - and vanity - of her subjects. For all the worthy claims made about her work ("Identity" and "Power" are the key buzzwords, signalling high moral purpose and serious intent) it is undercut by an anarchic wit, debunking the expectations of those who commission her. She stalks the corridors of power with a smile on her face.

n 'Care and Control' is at Hackney Hospital, Homerton High St, E9 to 5 Aug, Tues-Sat, 12-6pm