SOME years ago, a schoolteacher friend of mine described an event it would be hard to imagine occurring today. Newly appointed to the RE department of a school in the Home Counties, she found herself accompanying a group of pupils on a school trip to the Holy Land. As she and the students were getting off the bus outside Jerusalem's Old City, a wholly unexpected tableau materialised before their eyes, at once deeply strange and yet somehow utterly familiar.

On a dusty unmade track beyond the municipal car park, a man in traditional Bedouin dress suddenly appeared, riding on a donkey, and herding goats. It was as if the raw material for a parable was being assembled in front of their eyes, or a page from their illustrated Bibles back home was coming magically to life.

The girls immediately reached for their cameras, preparing to transform the living image before them into a badly framed cliché that would take its place alongside poolside snaps and photographic records of similar high jinks. At that point, the senior teacher intervened, suggesting that the girls should put down their cameras and simply look. 

IT WAS wise advice, which the historian Simon Schama would have understood instinctively. Announcing, this week, the forthcoming exhibition he has co-curated at the National Portrait Gallery, he bemoaned the idiocy of the now ubiquitous "selfie", suggesting that people's ob- session with their smartphones has made them prisoners "of their own headphones".

"We ought to be a community in which faces exchange looks," he went on, suggesting that we are in danger of shying away from the shared reality of human interaction in favour of a two- dimensional approximation of that reality, acted out beneath our downturned gaze.

The evidence, if we only look, is plain to see. On buses and trains; in cafés,and parks; even - get this - at the 11.30 a.m. sung eucharist in St Paul's Cathedral on Easter Day, people are routinely to be seen pecking away at their screens rather than experiencing the richness of what is going on all around them.

In fact, these days, we are inclined not to experience events at all; simply to photograph them. Without any concentration on what we are looking at, or consideration of the propriety or otherwise of our actions, we automatically raise the viewfinder and click.

If the latest edition of the French magazine Paris Match is to be believed, this phenomenon has now acquired troubling proportions. The magazine has confirmed as genuine recovered cameraphone footage of the harrowing final moments of the 150 passengers on board the Germanwings Flight 9525 that recently crashed into the Alps.

What compelled someone at the extremity of terror to photograph others similarly afflicted we can only guess at. In the same way, it is hard to imagine why bystanders not only photographed a suicidal man on a rooftop in Telford last month, but also encouraged him to jump, before posting the images on YouTube.

The camera, we are told erroneously, never lies. But on occasions it can, and increasingly does, corrupt.

Trevor Barnes reports for BBC Radio 4's Sunday programme.