The most enduring images break their immediate frames of reference and climb into our imaginations. Such is the power of a photograph captured this week of a soldier in the Free Syrian Army standing guard as the first major ceasefire in five years came into effect. The picture relies for its intensity on an illusion of three-dimensionality that makes us believe that the patrolling figure is on the verge of stepping through the lens of the camera into our very minds. The subtle sleight of eye is comparable to an optical trick played in the 19th Century by a Catalan illustrator, whose subject – like the rebel soldier in this week’s image – seems forever poised on a threshold between this world and another.

Among the challenges every photojournalist faces is how to bridge the geographic and cultural divides that separate his or her subject from an audience half a world away – an audience over whom a tidal wave of competing visual messages crashes every day. The perspective adopted by Ammar El Bushy, the photographer who took this photo of the anti-Assad guard, takes advantage of a perfectly positioned notch in the entrance-way of the tunnel through which the crouching figure is seen advancing towards the camera.

That notch in the rubbled wall of a bombed-out structure is curved around the shape of the soldier’s head, creating the unsettling illusion that the armed rebel is at once behind and in front of the aperture to the tunnel. The result is a photo that breaks down the barrier between the stresses of a conflict raging in an inconceivable elsewhere and the retinas of distant readers.

The photograph’s ability to overcome visual boundaries places it in a tradition of aesthetic trickery that dates back to ancient Greece and a technique now known by the French phrase trompe-l'œil (or ‘deceive the eye’). El Bushy’s image recalls, in particular, the optical dexterity of a work by a pioneering 19th-Century Realist painter from the Catalan town of Puigcerdà. Pere Borrell del Caso’s most famous work, Escaping Criticism (1874), depicts a boy in mid-clamber, as if burgling his way through the painting’s frame – his eyes wide in wonder with his first glimpse of the real world. Seen in the context of this week’s war-weary photograph, Borrell’s enchanting canvas interjects a note of hopeless hope, that the ceasefire into which the rebel tentatively steps is more than a cruel illusion.

100 Works of Art That Will Define Our Age by Kelly Grovier is published by Thames & Hudson

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