Our culture is hungry for stories of buried treasure, for the lost archive. So when something of startling value is brought blinking into the light after many years, it answers a romantic urge. Of course it doesn’t happen much any more, not in a digitised e-culture in which, like Puck in A Midsummer Night’s Dream, you really can put a girdle round the Earth in no time at all. Something interesting has just cropped up in Italy, mind.

Visit the room in the Louvre where the Mona Lisa hangs, and all you will be able to see is a glass-covered rectangle and hundreds of camera phones held high. Certainly you will be unable to examine the woman in the picture, or contemplate the work of the artist who painted her. Yet they - sitter and artist - are, finally, what matters: that one day, the (probable) Lisa Gherardini, wife of a silk-merchant, sat down in front of an artist, who began to paint her.

Camille Silvy may be the least recognised of all the great photographic innovators of the 19th century. After a decade of almost ceaseless technical innovation, and astonishing output as the society portrait-photographer of the 1860s, he abruptly closed his London studio, aged only 34, returned to France, and, after a brief stint in the garde mobile in the Franco-Prussian War, spent much of the rest of his life in and out of asylums.

What a troubled life Alice Neel led. The death of her first child, a daughter, who died of diphtheria in 1928  just before her first birthday; another daughter lost to her estranged husband’s family in Cuba two years later (as an adult and a mother herself, the daughter, Isabetta, committed suicide); life as a single mother raising two later sons on welfare in the slum district of New York's Spanish Harlem; and a neglected but always diligent artist for much of the rest of it, only achieving fame and acclaim towards the end.

Aptly, this new documentary about how the Rolling Stones fled from England to the South of France to record Exile on Main Street was premiered at the Cannes Film Festival, with a supernaturally healthy-looking Mick Jagger on hand to give it a promotional shove. Jagger (along with Keith Richards and Charlie Watts) produced the film, working closely alongside director Stephen Kijak to knit together an evocative and emotional portrait of "the greatest rock'n'roll band in the world", at what many would argue was their peak.