For a split-second, everything falls into place, the occasion, the movement and the light combining to produce a picture that is much more than a mere photograph.

Bobby Moore holding up the World Cup in 1966. Charles and Diana's balcony kiss. The image of St Paul's during the Blitz. What price can you put on photographs such as these? Indeed, what price an entire collection?

The answer, it seems, is $2.4 billion (£1.2 billion) - the amount agreed by Hellman & Friedman, the private equity firm, to buy the archive of Getty Images, one of the world's best-known picture libraries. The collection has about 70 million pictures and 30,000 hours of film footage.

Getty's historic Hulton Archive has photographs dating back to the early years of photography in the mid-19th century. Taken as a whole, it is a photographic encyclopedia of a century, with images by acclaimed photographers, which include Man Ray, photographs of the Vietnam War and a selection of iconic shots of Audrey Hepburn.

Getty's shares have fallen 41.5 per cent in the past year, partly the result of concerns about new competition - not from industry rivals but from the general public, who, armed with camera phones, are supplying free or cut-price pictures by the million.

Jonathan Klein, co-founder and chief executive of Getty Images, said that the board had “determined that this outcome is in the best interests of our stockholders as it provides them with superior and certain value”.

Sources close to Hellman & Friedman said the private equity group planned to focus more heavily on exploiting Getty's archive through the internet and other digital channels.

The sale represented a premium of approximately 55 per cent more than Getty Images' closing price on January 18, the last trading day before the company announced it was exploring strategic alternatives.

Getty was advised by Goldman Sachs and financing was provided by Barclays Capital, GE Commercial Finance and RBS Greenwich Capital.

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