It's not exactly Smell the Glove, is it? In the world's greatest rockumentary, This Is Spinal Tap, the fictional heavy-metal band's woes deepen when supermarkets refuse to display the sleeve of their latest album with its offensively sexist imagery. Instead, it is sold in a plain black sleeve, just as Manic Street Preachers' new album is now to be displayed by British supermarkets in a plain slipcase.

But there the comparisons end. It's hard to imagine the chain of decisions that led to Jenny Saville's painting of a boy's face in colours that vary from olive green to reddish brown, blue and black, being judged too offensive to go on public view. The painting can apparently be interpreted to show blood on the boy's face – although as the band rightly point out, this is a subjective view. He might have crimson scars and battered lips; or these might just be the colours Saville has used to evoke the appearance of flesh. The whites and creams, the blues of his eyes, are just as shocking.

Saville's fans – who evidently include the Manics as this is the second time they've used her work – see her as this century's Lucian Freud. Be that as it may, the impact this picture has made raises the interesting possibility that hand-made, painterly images now have more power to shock than conceptual artworks. Everyone is used to seeing dead sharks. The point about photographic art is that it's quite simple, really, whereas a painting can raise all kinds of troubling ambiguities.

For me this is a painting of psychic hurt, a portrait of pain. In that sense it is truly troubling – but to see it crudely as an image of a child who has been hit (which must be the supermarkets' view) is to impose your own subjective interpretation. Paint creates uncertainty. It is genuinely impossible to know if those red marks are bloody scars or expressive smears. In the end, what has caused offence is the intrusion of emotion and artistic depth into the temples of commercial banality.