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The series of photographs were taken during one day in 1968.

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The photos were taken in three London locations: Old Street Station's roof, a park in Highgate and on the banks of the Thames.

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Go on lads, give us a smile...

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...that's better.

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Time magazine thought this snap was too "spooky" to use on the cover when John was murdered.

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During the rooftop shoot, Paul nearly fell off.

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Paul didn't notice Tom Murray taking this picture...

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...but he plays up to the camera when he realises he's been caught on film.

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Not the Fifth Beatle.

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Paul is punished for Rupert and the Frog Song.

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The photos are now worth an estimated $2.3m. The exhibition runs at Liverpool's Matthew Street Gallery until the end of June.