Today, it seems, the camera almost always lies. Yesterday, in what must count as a rather spectacular own goal for Procter and Gamble Ltd, we learned the real secret to Twiggy’s “brighter-looking eyes” – airbrushing. Not the Olay Definity eye illuminator, as she claims in the advertisement.

When questioned by the Advertising Standards Authority, the company admitted “minor retouching” during “post production work” in the eye area.”

This could be the understatement of the year. The ad features a woman who could be in her 20s, with a smooth flawless complexion.

The irony is that Twiggy, pictured, is an attractive middle-aged woman who has done nothing to hide her age. In fact, her natural beauty, complete with laughter lines and slight bags under the eyes, has done wonders for M&S sales in recent years.

This story is a sort of reverse Dorian Gray parable. In the Oscar Wilde original, the eponymous

central character retains his youthful beauty, while his painted image in the attic does all that unpleasant ageing for him.

In the Olay ad, this woman, who embodies the notion of ageing with dignity in real life, has been returned to her youth thanks to some technological wizardry. The ASA ruled that the result “could give consumers a misleading impression of the effect the product could achieve”. I’ll say.

It is a triumph for the campaign being waged by East Dunbartonshire LibDem MP Jo Swinson, who collected more than 700 signatures on her online petition complaining about the “digitally re-touched” image.

Retouching photographs is as old as photography itself. No Daguerreotype portrait was complete without a spot of hand-tinting. Cecil Beaton routinely doctored his famous society portraits. In the flesh, Marilyn Monroe never quite lived up to those ravishing images by which we know her now.

Celebrities are usually more than happy to consent to a little sleight of hand in their published images.

Kate Winslet complaining at being slimmed down on the cover of GQ magazine in 2003, or Keira Knightley wryly observing that the D-cup boobs on her poster image for King Arthur appeared to have been transposed from someone else, remain rare exceptions.

Let’s face it, we’re all doing it aren’t we? Who hasn’t quietly censored photos that show us with a double chin or cellulite? And since the arrival of Photoshop and Picassa, we can all enhance our holiday snaps. Liz Hurley cheerfully admitted doing so recently. But there is a difference between gentle flattery and the misrepresentation of a woman’s appearance that has become routine in the magazine world.

Let me put you in the picture. As the circulation battle in the declining glossies market has intensified in the past decade, these images – especially cover shots – have strayed further and further from reality.

Some models have such pronounced cheekbones and long thin legs that they look more like aliens than women.

Ignore anyone who tells you that Size Zero models are no longer fashionable. A friend who does fashion work for Vogue and other fashion mags admits that she not only removes spots and blemishes but often shaves a few inches off waists of already tiny models and gives their tummies the “ironing board look”.

Crude airbrushing is obvious. It creates a look known in the trade as “plastic fantastic” but in the hands of a skilled retoucher it may be impossible to detect. This is more than annoying and depressing for those of us who have to live with our imperfections and for self-conscious teenage girls these pictures peddle the dangerous lie that there is only one version of human beauty.

They should be able to deconstruct these images and deal with them rationally but they are not only powerful but ubiquitous.

When 70% of teenage girls say their idea of the perfect body shape is influenced by magazine images, no wonder so many now suffer from anorexia and body dysmorphia (the conviction that they are ugly). We have reached a point where the only “real” images we see of celebrities are when they fall from grace and magazines rush to mock their flaws.

What effect do airbrushed images have on ageing women? Psychoanalyst Susie Orbach says that it encourages us to think: “I ought to fix myself.” One American study showed women felt much worse about themselves after viewing magazine adverts for just three minutes. At the very least this damages self-confidence and self-esteem. In extremis, it leads to constant dieting and unnecessary cosmetic surgery.

When Baroness Kingsmill looked at airbrushing for the British Fashion Council two years ago, she concluded that it could “perpetuate an unachievable aesthetic”. Jo Swinson is a brave lady to take this on. (Try Googling her and you’ll find a tricked-up image of her looking like a blonde Barbie doll from the satirical Red Rag website.)

Swinson is so concerned about the impact of manipulated images on depression and eating disorders in young girls (and increasingly in boys too) that she wants such advertising brought under control.

This is unlikely to happen, not only because the ASA receives relatively few complaints about airbrushing but also because of the difficulty of drawing the line between an enhanced image and a natural one when lighting, make-up and computer graphics all have an effect on the way models appear.

Swinson’s argument is that if advertisers were obliged to admit they used airbrushing, consumers would realise that they don’t need to measure up to something that is essentially fake. Meanwhile children, who easily confuse fact and fantasy, need to be taught a measure of media literacy.

In Victoria, Australia, a voluntary code of conduct discourages the use of Photoshop to alter images of women. In Sweden, a government website shows young women how images can be altered by airbrushing and retouching. And a bill currently going through the French National Assembly would require warnings on retouched photos used in newspaper editorial as well as advertisements. In Britain too it’s time to get real.