The camera is a superb liar. It only shows one moment, and has no obligation to explain the bigger picture behind it. The selective use of photographs can therefore replace truth with whatever visual detail we choose to fix on. Horror or schmaltz, the effect is the same, to simplify reality and turn a story into a deceptively straightforward image.

In the 1930s and 1940s the dishonest manipulation of photographs was a speciality of state propagandists. Backroom technicians in totalitarian darkrooms removed unwanted faces from pictures and turned emotive images into posters. Today, we don’t need propaganda machines to deceive us because we can make hypocritical and self-manipulating choices ourselves just by “liking” the pictures that show us what we want to see and ignoring those that are more awkward.

The protests in America against a grand jury’s decision not to indict white police officer Darren Wilson for shooting dead unarmed black teenager Michael Brown in Ferguson, Missouri, have thrown up a sickly sweet instance of this modern dishonesty.

Of all the disturbing images of streets on fire and crowds unappeased that have seethed since the grand jury decision in Ferguson set off protests across America, one of the most popular online turns out to be a touching moment of interracial togetherness. You heard me. Like a supermarket Christmas ad, this photograph taken at a Ferguson protest in Portland, Oregon, feasts on a moment of truce and peace amid the anger.

It shows 12-year-old protester Devonte Hart sobbing as he hugs a white police officer. The officer’s face too is tenderly emotional. The cop appears to be comforting the boy. After all the anger, all the divisions, here is a moment of human reconciliation.

What nonsense. It is one moment among many, and the choice to look at it and celebrate it is clearly a choice to be lulled by cotton candy. It has got more than 400,000 Facebook shares. Each one of those shares is a choice of what to see and what not to see. In the context of the completely unresolved and immensely troubling situation, not just in Ferguson but across the United States, where Ferguson has opened wounds that go back centuries, this picture is a blatant lie.

A picture does not have to be staged to be a lie. It just has to be massively unrepresentative of the wider facts and enthusiastically promoted to iconic status in a way that obscures those facts. This photograph, which first appeared in the Oregonian newspaper, was taken after Hart stood on the protest line with a banner that said “Free Hugs”. Portland police sergeant Bret Barnum got talking to the boy and asked if he could have a hug as well.

What a photo opportunity. In terms of straight news values, this tender moment offered a bit of variety from glum scenes of protest. Yet it instantly had a deep appeal to those looking for a soft focus view of race in America.

A woman in the background is taking her own picture of the warm scene. She can’t wait to share it. What a heart-stopping, iconic, totally emotional photograph. Add a weeping emoticon or whatever seems eloquent to you.

Sentimentality used to be the preserve of musicals and Hollywood: now it shapes the news. Photographs are no longer carefully chosen by newspaper picture editors to craft the story. Of course, the traditional media are no strangers to manipulating reality – consciously or unconsciously – with photographs. But when news images are given life and meaning by the number of times they are shared on Facebook, the only editorial control is sentiment. This picture is cute, therefore popular, therefore true.

Has truth itself become a popularity contest now? Countless photographic images are produced every day, recording multitudinous events. The process by which a few of those pictures become “iconic” is not rational and does not have any responsible superego in charge of it. It surely seems absurd – given the seriousness of what happened in Ferguson – that a nation’s new, yet old, encounter with its most destructive division can be summed up by this soppy picture of a tearful hug.

Liking this picture as a definitive image of America’s race crisis is the equivalent of locking yourself in and turning up the volume to weep at Frozen while the streets are burning outside. Which is exactly what white Americans apparently want to do. Truth is a flimsy thing. It can be destroyed by a hug.