“Photography is a refuge for failed painters,” declared the French poet, Charles Baudelaire around 1862. Yet photography took over a century to become a genuine family member of the art world. The British Library was slow to capitalise on the visitor value and historical significance of the vast photo-archive that it accumulated over the birth-period of this new artform. But its spectacular debut exhibition has burst open the vaults containing over 300,000 images, and now presents a magnificent production leading visitors on a journey back through time as the new art form was gradually building momentum.

West Coast pop art always was a poor relation to the world-beating New York original. Beside the Big Apple titans – Andy Warhol, Roy Lichtenstein and Claes Oldenburg – LA painters such as Ed Ruscha, Robert Irwin and John Altoon remained essentially local figures. Or that’s certainly the way it has looked from this side of the pond.

Does a winning photograph jump out at you? Sure, we can talk earnestly of composition, an interesting subject, a telling juxtaposition, or the abstract interplay of colour, texture and light. But perhaps more than any other visual art form, what strikes us most about a photographic image remains somehow more elusive. And the hand of the artist who presses the shutter, rather than wields the brush, is not so easily perceived.

By all accounts Eric Gill had a shocking private life. When it was revealed in Fiona MacCarthy’s biography, published 20 years ago, that he’d embarked on an adult incestuous relationship with not only both his of sisters but, later, with two of his teenage daughters (the family dog didn’t escape his attentions either), there were demands from some Catholic churchmen for the prompt removal of his carved stone altarpieces.

Damien Hirst's new exhibition at the Wallace Collection is evidence of a deal between nervous guardians of the past and a contemporary artist seeking to burnish his future historical credentials. It stinks. Entitled No Love Lost, Blue Paintings by Damien Hirst ­ - the clunking allusion to Picasso's Blue Period marks out the scale of Hirst's ambition -­ it presents 25 paintings that we are assured are actually by Hirst rather than a cohort of assistants.

Is site-specific the new collaboration? What I mean by this is that where it was once the fashion for artists and dancers (think Robert Rauschenberg and Merce Cunningham) or film directors and opera houses (Anthony Minghella and the ENO) to mix art forms, now it is fashionable to have work inspired by and installed in a particular place.

That artists didn't just respond to the rapacious commercialism of the late 20th century, but actively contributed to it is hardly news. That the marketing of art can be part of the art itself  is something everyone now implicitly understands, even if it’s only through hearing Tracey Emin wittering about herself on television.

History is written in blood, however elegant the cover. Nowhere is this more apparent than in the collapse in 1521 of the Aztec Empire, a culture that presented Europe with a vision of such otherness that it could only be destroyed. In 2002, the Royal Academy of Arts tried to persuade us to look beyond the grisly tales of human sacrifice to a more nuanced portrait of a people steeped in gory rituals that we, soaked in the serial-killer television porn of the 21st century, might strangely understand.