Tesco’s face-scanning system, courtesy of Quividi, means we’re being watched and profiled - sometimes just so we can be shown adverts. Can’t we be left free just to be ourselves?

A man walks into a bar. A screen says: “You’d like a pint of beer.” It’s right. Welcome to 21st Century retail, Minority Report-style.

Tesco’s announcement this week that it’ll be installing face-scanning advertising screens in all its 450 petrol stations has detectably raised eyebrows and hackles among many of us who don’t necessarily mind watching a screen, but really don’t want to be watched by one.

The screens are part of an ad network managed by Amscreen, part of Alan Sugar’s business empire run by his son Simon. They use technology from Quividi, a Paris-based company specialising in identifying people’s gender and age from video images.

Amscreen uses real time data about who’s watching the screens supposedly to target ads at the most receptive audiences, presumably touting golf clubs and power tools to the chaps, and perfumes and soft furnishings to the ladies. Adjust by age segment to plug alcopops, life insurance, Miley Cyrus and SAGA holidays. Everyone’s a winner in the world of stereotypical marketing demographics.

The age of liberty

So will Sugar’s screens steal our souls as we bask in the glow of exquisitely well-targeted ads while we queue to pay for our Tesco unleaded? Quividi flatly denies that its system identifies anything more than the gender and approximate age of each viewer, alongside time and location data.

The company told the Guardian: “It can detect if it’s seeing a face, but it never records the image or biomorphological information or traits.” If true, this lumps every individual into one of just eight categories (two genders multiplied by four age bands). This isn’t enough information to track specific people returning to the same location or visiting other shops.

But we’ve only got the company’s word for it. Neither Tesco, Amscreen nor Quividi appears to have done a privacy impact assessment as recommended by the Information Commissioner’s Office for systems where “new and intrusive technology is being used, or where private or sensitive information which was originally collected for a limited purpose is going to be reused in a new and unexpected way”.

An independent privacy and security audit of this novel and potentially intrusive system that confirmed its relative innocuousness would be even more reassuring.

From spam to surveillance

From their own perspective, Amscreen and Quividi depend on accurately classifying each person so that ads can be better targeted. So the temptation to retain the video footage and the encoded templates of each person’s facial features must have been hard for Amscreen resist - if indeed it has been.

Keeping this data would provide the opportunity to refine every step of the classification process using big data techniques that would be useless on smaller sample training data sets. One of the reasons that cloud-based email services such as Gmail are so good at filtering out spam is that they get to chew continuously on huge, real-world datasets. With Amscreen’s system claiming an accuracy as low as 50% in some situations (women wearing baseball caps), there’s clearly much more work they’d like to do here. Retaining more data from the screens’ projected audience of five million UK adults would make that task much easier.

Now, if all these screens do is put us all into one of eight anonymous boxes, then it seems that we don’t have much to worry about. But the impact of a surveillance system needs to be considered in context, not in isolation.

A Tesco forecourt: your numberplate is the first thing that gets scanned. Is your face next? Photograph: Peter Macdiarmid/Getty Images

Supermarket society

The typical British supermarket is already a near microcosm of a total surveillance society. CCTV catches your face from before you enter the building to the moment you leave, and that video is retained. If you pay with plastic rather than cash then that gets logged by the retailer, your bank and the card processing network. Tesco pioneered the store loyalty card, and if you use one of those you’re asking to be data-mined for everything from your household composition, health and dietary preferences to identifying and even predicting life events like holidays, new children, marriage, separation and ultimately, death (at which point you rather selfishly stop being a customer). Various systems track customers in store using their mobile phone signals.

If you’re buying petrol on the supermarket’s forecourt you can expect to have your vehicle registration logged by automatic number plate recognition (ANPR) cameras. What you might not expect is that some commercial ANPR data gets shared in real time with the police, although we’re not allowed to know exactly where this happens.

Dropping face-scanning cameras into this kind of environment is adding another heavy-grade weapon to the retail surveillance arsenal, even if it’s currently used to fire blanks rather than lethal ammo. Once we get used to seeing them, or rather, once we get used to not seeing them, that huge untapped potential for further intrusion is just a software upgrade away. Given the supermarkets’ apparently insatiable desire to know everything about our lives, who’s to say that the intention isn’t there? The capability certainly is.

We tolerate the sheer quantity of advertising in shops, on public transport and in the street because much of it, being only loosely targeted, really isn’t that good. As static posters give way to moving video and interactive screens that can be much better targeted and therefore much more capable to compel our attention, we need to reassess just how much of it we can tolerate as individuals and as a society.

While Edward Snowden’s revelations have made many of us think more seriously about surveillance (though not enough about the inextricable link between government and corporate snooping), we give little thought to the ways in which corporations have commandeered our thoughts.

Freedom to think of nothing

Where are the moral limits of marketing and advertising? If we visit Tesco, does the store own our brain for the duration of our visit? Or should we expect to be left alone with our thoughts while we queue at the checkout? Which influence techniques should be considered unethical, whether due to their nature or their scale, when applied to a captive audience in a queue, on a bus or on a train - or indeed in a school, a prison, a hospital or a public toilet?

Our interstitial freedom - the ability to be unobserved and to think for ourselves in the gaps between surveillance and influence systems - is shrinking daily. No matter how little that freedom is further eroded by Amscreen’s cameras and screens in Tesco today, the travel is all in one direction. It needs to be resisted and rolled back. Meanwhile, we must resort to customer tradecraft: Don’t leave home without a cap and a good book.

Adrian Short is a software developer and data analyst

• Q+A: What Quividi’s face-scanning system does and doesn’t do: talking to its chief operating officer