Second-hand pose

Thomas Ruff 1979 to the Present Tate Liverpool, until 6 July

'WHAT I produce,' Thomas Ruff once categorically declared, 'is art.' What Ruff produces, in fact, has mostly been pre-produced by others: newspaper photographs removed from context and grainily blown up, political posters collaged together from the same grubby archives, surveys of the night sky borrowed from an astronomer's telescope, and smeared, viscous scenes of copulation downloaded from the Internet. Given the scavenged and second-hand nature of what he produces, you can see why Ruff - who is German, and therefore given to the utterance of edicts - might insist with such self-righteousness on his status as an artist. It's just not a statement you can conceive of Picasso finding it necessary to make.

Another meaning, as it turns out, echoes portentously behind his statement. In Ruff's estimation, what he produces is art as opposed to photography. His reasons for this self-assessment are academic: 'I received my training at an art academy, so that's what is artistic about my photographs.' Why - I earnestly asked myself as I stared at Ruff's vacuous coin-booth portraits of friends and his grandiosely glossy snaps of dull factories and empty bedrooms - should these photographs not be thought of as photography? The answer, if you are prepared to swallow it, comes from Ruff's critical apologists. His photographs are art because they quizzically reflect on the process of image-making; to quote one of his learned promoters, they embody 'the gaze's pre-reflexive indistinctness, suggestively embroiling volatility, synthesising projection, subliminal violence, as it strives to identify'.

(That sentence, I should add, was originally written in German.)

My own gaze, trained on Ruff's images, sees only a world that is not worth looking at. Grimy tower blocks in Düsseldorf, monumentally enlarged, surrounded by patches of downtrodden grass; empty concrete forecourts outside boxy office buildings; desolately neat interiors with shiny wash basins and smooth, straightened candlewick bedspreads. Ruff defends this banality by asking a rhetorical question: 'If things are the way they are, why should I try to make them look different?' Because - I would suggest - that is what art does, or what it used to do before it was overcome by postmodern self-congratulation.

Having announced that he is an artist, Ruff promptly inscribes himself in the history of art. A small room at the Liverpool Tate's exhibition is devoted to predecessors whose influence he acknowledges. The line-up begins, astonishingly, with portraits by Bellini and Cranach, even though Ruff's portraiture lacks both the beatific beauty of the Italian and the warty, idiosyncratic grotesquerie of the German. Ruff's subjects share his anaesthetised blandness. Their skin is waxen, their mouths zipped up tight, and in their eyes, rather than any reciprocal evidence of emotion, you see only the reflected glow of the lights Ruff set up in the studio. Not even their blemished skin humanises them; they might have emerged from pods. It is quite an achievement to make your intimate acquaintances look so uninteresting, though I suppose it can be managed with the aid of what the catalogue calls 'a rigorously conceptual resolve'.

In the section devoted to newspaper photographs, Ruff's bored and undiscriminating vision becomes offensive. Lenin reads Pravda , Marcos harangues a crowd. Missiles are launched, and a group of grinning soldiers hold up the severed heads of enemies. No captions identify the subjects, or summarise the stories attached to these visual anecdotes. Ruff invites us, as if that were enough, to admire the grey granular texture of the newsprint. But what about the image with a swastika, and a gang of goose-stepping workers whose arms are stiffened in a salute? There are no names, no dates, and consequently no need to worry about the Third Reich: Ruff, born in 1958, belongs to a generation that has taken refuge from history by cultivating a merciful amnesia.

His mocked-up political posters are presented as trib utes to John Heartfield, the artist who so pluckily baited the Nazis. But there is a crucial difference. Heartfield - who anglicised his family name, Herzfeld, in order to expunge the shame of being German - believed that his defamatory images could help the cause of resistance. Ruff depoliticises his posters by obscuring or inverting the slogans attached to them, so they must be read as designs, not graphic protests. His drab factories and nasty petit-bourgeois flats joylessly deride another modernist dream of engineering a better world. This is what has become of the Bauhaus, or of Mondrian's belief in the imminence of the earthly paradise. Instead of a geometrical utopia, we have only the tiled walls and scrubbed enamel of these suburban bathrooms.

It all recalls the antiquated, affectless irony of Andy Warhol, whose tabloid headlines announcing plane crashes or deaths in the electric chair laughed at the uncoolness of emotional empathy and the irrelevance of a social or political conscience. At least the zombified Warhol, imitating the demeanour of the undead, knew himself to be a freak or a mutant. Ruff humourlessly paraphrases Warhol's jokes, as when he says that, in using the camera, he is 'letting the machine do the work it would do anyway'. Our eyes, which are corporeal cameras, promiscuously go on doing the work of seeing that they would do anyway; in Liverpool mine slid away from Ruff's tableaux and strayed to the windows of the gallery to admire the rusty brick fortifications of the Albert Dock and the hackles of the waves on the windy Mersey. Reality can still supply visual stimulation, even if contemporary art makes you want to lower your lids in despair.

Laura Cumming is away