杏吧原创

IT鈥橲 Sunday afternoon in London鈥檚 Trafalgar Square. Not far from the fountains, someone has left an enigmatic message on the steps: 鈥淔ine mist washes over my face,鈥� it reads. 鈥淕ray skies seem bluer here.鈥� Tourists wander by, but none of them can see the words.

In fact, there are hidden messages painted all over the square. On the side of the National Gallery, somebody has scribbled a declaration in large letters: 鈥淢aria, I love you鈥�. That graffiti has been there for more than a month without anybody cleaning it off. And inside a nearby restaurant, waiters are serving pizza, blissfully unaware of the message on the wall saying the food looks like pigeon droppings. The square is home to invisible images too 鈥� and even strange creatures. A yellow pufferfish, for example, is floating in the air above a metal sign, blowing bubbles.

Visit any major city, and you will find it teeming with similar messages and images. For the past few years, millions of people have been using location-aware smartphone apps to daub comments, ratings, images and videos on top of places, objects and, to a certain extent, even themselves. This digital graffiti is personal, informative, sometimes trivial and often subversive. And soon it will be thrust into much clearer view. Later this year, Google is expected to launch a set of 鈥渁ugmented reality鈥� glasses that can overlay digital information onto the physical world. Apple is also rumoured to be investing in such technology. One of the upshots will be that the digital graffiti people have been creating for the past few years will become increasingly visible. It鈥檚 a development that is poised to disrupt business, challenge the law and transform how we navigate the world.

People have daubed messages and tags onto physical places since at least the 19th century (see 鈥�Digital nomads鈥�). But they only began writing onto the world digitally in a big way in the past decade, when smartphones equipped with GPS location-tracking arrived. The first thing this technology allowed people to do was add reviews to restaurants and other spots they visited. Those with the app Yelp, for instance, can whip out their phone to reveal hundreds of comments left by fellow users attached to points of interest in the vicinity.

Then people began to tag the physical world as part of their online social life. Take the popular smartphone app Foursquare. It encourages people to 鈥渃heck in鈥� as they arrive at a bar or other venue, sharing their location or leaving local advice for friends. The status updates on social networks like Facebook and Twitter can also be geotagged, meaning that people share not only what they are doing, but where. A smartphone can display a map of people tweeting nearby, for example.

Now apps are emerging that explicitly trumpet their ability to tag the physical world like graffiti. One comes from Caterina Fake, a co-founder of photo-sharing website Flickr. Her new app, , allows users to leave photos, videos and text at any location they want. Some might be memories, like the scene of a first kiss, others are tips like where to find the best doughnuts in the area. 鈥淎ll of these stories and information and gossip and history are actually already there,鈥� says Fake. 鈥淚t鈥檚 just never had a way of making itself known.鈥�

At the moment, smartphone users see most of this tagging as pins on a map of their vicinity. But increasingly, it is becoming possible to see the digital notes that people leave behind superimposed over the world as graphics 鈥� or 鈥渁ugmented reality鈥� (AR).

AR has come a long way since the term was coined in the 1990s by Tom Caudell and David Mizell at Boeing. They designed a heads-up display through which computer-generated graphics were incorporated into a person鈥檚 view of the physical world. It was initially seen as a tool for aiding people in manufacturing, but it soon became apparent that such devices could overlay any scene with any kind of information.

Achieving that vision of an augmented world has proven more difficult technically than many hoped, but smartphone technology has brought it a step closer. Location-tracking via GPS was the start, but when phones began to incorporate cameras and compasses a whole host of AR apps and games emerged. You peer at a scene through the device鈥檚 camera, and see graphics laid on top of it in real time. Yelp users, for instance, can see star ratings floating over the restaurants in front of them.

Integrated world

More recently, it has become much easier for individuals to create AR overlays themselves. An app called enables people to add photos, videos and animations to anything they care to augment: buildings, signs, statues and so on. Aurasma claims to have more than 3 million users already. Central London, for example, features augmentations ranging from YouTube clips to animations of Batman.

To add one yourself, you first snap a photo of a scene, say a brick wall. Then you search your phone鈥檚 memory, the internet or the app鈥檚 library for a digital layer 鈥� perhaps a video you had recorded 鈥� and position it over the image of the wall using the touchscreen. People nearby who have the app will then know it is there because they can see local augmentations on a map. If they visit the same wall and look at it through their phone camera, Aurasma will display your layer 鈥� in real time. 鈥淓veryone uses the app for a different kind of thing,鈥� says Tamara Roukaerts of Aurasma. 鈥淚 take videos of my son and leave them around the house. I can see videos from a year ago in the place where they were taken: it鈥檚 a window on the past.鈥�

The major downside with such AR apps is the need to view this digital world via a small screen. But there are signs that augmented reality is poised to enter much wider use. Earlier this year, Google announced it is developing a headset worn like glasses that displays video, graphics and text. Apple has also filed a series of AR-related patents, hinting that it may have a device of its own in the pipeline.

If such eyewear becomes widely available, it will allow for the seamless integration of the physical and digital world, with no need to log into individual apps to see what is around you. All the information would be displayed automatically: clouds of comments, images and other ephemera popping up as you walk down the street.

So if the era of seamless AR is at hand, what will be the consequences when the rest of the world sees all the digital tags people have created? For a start, it will have a disruptive effect on business and the law. It might be tempting to see digital tagging as harmless 鈥� it is certainly easier to avoid or remove than actual paint 鈥� but not all of it is benign.

Consider this case featuring the oil giant BP. In 2010, , an artist, released an AR app called 鈥溾�� in response to the Deepwater Horizon oil spill. When users pointed their phone鈥檚 camera at any BP logo, it became augmented with a broken pipe spewing out oil. Naturally, BP was not happy. 鈥淚t was cited by trademark lawyers as the first example of a logo hack,鈥� says Skwarek.

In another of his projects, called protestAR, Skwarek managed to tag a place that was otherwise off limits. During the protests carried out by the Occupy movement in the US last year, many parts of New York City were cordoned off so people could not protest there 鈥� particularly around the New York Stock Exchange. So Skwarek staged an instead. Anyone visiting this part of the city, even today, can switch on their phones, and via an , see the street teeming with images of protesters accompanied by raucous chants.

These augmentations might be seen by many as nothing more than mischievous stunts, and today you have to make an effort to view them. But they illustrate how digital tagging could be unwanted in the eyes of some people. It is conceivable that offensive digital imagery could be plastered onto a school or place of worship, for example, and in a seamlessly augmented world such tags may be harder to avoid. The internet reflects all aspects of human nature, including the darker side. If that unpleasantness became visibly attached to physical places, it will surely test our notions of freedom of expression.

According to James Gatto, a technology lawyer at legal firm Pillsbury, based in McLean, Virginia, there are no specific laws in place to stop people from placing digital tags wherever they want, as long as they are not defamatory, threatening or in breach of copyright.

鈥淚t is tempting to assume that placing digital tags on buildings is harmless, but not all of it is benign鈥�

Still, eventually the law may be forced to adapt, says , chair of Ethics and Emerging Technologies at the University of the West of Scotland in Paisley, UK. That might mean that building owners have a right to demand that app designers erase unwanted tags. 鈥淲e might even 鈥榳rite protect鈥� buildings so only those with ownership of the property can add layers of content,鈥� he says.

There are some signs that app designers could also put in place technical barriers to prevent people from augmenting certain things and areas. For example, if companies so wish, they can already stop people annotating their logo using the Aurasma app. Right now, though, it would be virtually impossible to bar the augmentation of a particular place from all apps 鈥� there are simply too many to block.

As digital tagging of physical things continues to converge with AR, another implication worth considering is what it could mean for all the data that is already 鈥渁ttached鈥� to individuals. In one vision of an augmented world, a person鈥檚 online activity and other details could be visibly linked to them 鈥� their social network activity floating like a cloud above their head as they move around, for example.

Some people might not want that kind of link, but it could have its uses. After all, being able to visibly see a person鈥檚 online persona while at a conference or party, for instance, might help spark a conversation.

That potential might turn sour if people lose control of the details that others can see about them. Some of the issues that such technology raises were brought into focus earlier this year with a controversial smartphone app called . It wasn鈥檛 AR per se, but it did allow its users to identify people around them along with their digital annotations. In particular, the app told people about the 鈥渉ot girls鈥� in their vicinity, by using information from Foursquare. And if the women had not made their Facebook profiles private, it also allowed users to see their interests, photo albums and even telephone numbers.

Tagged people

Of course none of the women had volunteered any information for this purpose. So a woman might have checked into a bar nearby using her Foursquare app, oblivious to the fact that round the corner, a Girls Around Me user was browsing through her holiday snaps. None of this is illegal, but many people felt it crossed a line. Whether or not you agree, the furore it caused was enough for Foursquare to block the app from using its data. It was also pulled from Apple鈥檚 app store.

One day, we might be able to add AR tags to other people, and the tags would then follow them around for all to see. This might have its uses, but , co-creator of location-based app Geoloqi has pointed out that such a development could also enable new forms of bullying. For example, a child might attach the equivalent of a 鈥渒ick me鈥� sign to a classmate, she says.

For better or worse, the convergence of these technologies is poised to change how we interact with one another, says Nilesh Zacharius, an online privacy and policy consultant based in New York. 鈥淭oday, many of us assume that there exists a separation between our online and offline lives,鈥� he says. 鈥淭he advent of social media began to blur that divide, but augmented reality has the potential to shatter it completely.鈥�

In the meantime, at every moment the world is filling up with digital annotation. We are already swimming in it, and soon a bigger question may be how to filter it down.

Back in Trafalgar Square, the tourists remain unaware of the tags and ephemera floating around them. By the time many of them visit again, the city will have revealed itself in all its multilayered madness.