Last autumn at Tate Modern an image of the actress Brooke Shields, aged 10 and naked, was withdrawn from the exhibition Pop Life, after a visit from the Obscene Publications Unit. Spiritual America, by the artist Richard Prince, is a photo taken in 1982 of a photo taken in 1975, by the commercial photographer Garry Gross, of the young starlet made up like a grown woman.
The work is deliberately provocative, its aim is to question sexualised advertising images. After the police advised that it was "indecent" under the Protection of Children Act 1978, the gallery swiftly removed it, even though it had been on show at the Guggenheim Museum in New York without any complaint. Other images in the show that used pornography were not an issue.
This is far from an isolated case. Photographs of children are both the most common and the most controversial images of our times. While pictures of sex and death, traditionally taboo subjects, proliferate, a relatively innocent snapshot of a child brings in scandal. In a liberal age, it is the last redoubt of censorship.
A few years ago, a photograph by the artist Nan Goldin, Klara and Edda belly-dancing, had been on loan to the Baltic Gallery in Gateshead, for the exhibition Thanksgiving. The work depicts a joyful moment between two little girls, one is partially dressed and towers over the other who is naked beneath her. The picture was seized by police and removed from the show, which was then deemed incomplete and was closed.
What is significant is that it was a member of staff at the Baltic who phoned the police. The fears around potential accusations of child pornography are so great that galleries appear reluctant to defend the work and are trying to cover themselves in advance.
Pauline Hadaway, director of the Belfast Exposed photography gallery, is concerned, that "naked or not, exhibitions of children can be precarious, and what is OK or not can be arbitrarily decided. We are working in a culture of fear where one accusation can shut things down," she says.
This can have an impact on how cultural institutions operate. "In one instance we knew the artist, loved their work and knew they weren't going to do anything wrong," says Hadaway. "There was no risk, but because she works with young people going through adolescence, we were worried that we could be accused of something."
Instead of phoning the police, or censorship, they bit the bullet, commissioned the work and ran an exhibition by the respected documentary photographer Michelle Sank. "We went ahead when we realised that we were tearing our hair out about what ifs and had lost sight of the work," Hadaway explains. It was a success and the children involved loved the show.
Even with such support, Sank is worried that the climate of anxiety can also influence how artists operate. She feels that the concern about child protection, "has affected us photographers. It has made me more cautious, so I might not approach young people on their own, whereas I would once have talked to them and taken their picture."
How did we get here? The turning point was in the 1990s, which saw a dramatic shift in attitudes, exemplified by the hysterical response to the work of the photographer Sally Mann. Mann was already an established artist when she created the series Immediate Family, a collection of intimate portraits of her three young children, Emmett, Jessie and Virginia, who were all under the age of 10. The series made her name, but associated it forever after with controversy.
There was a media firestorm on the release of the book, including accusations of child pornography. One picture Virginia at four, was censored by the Wall Street Journal with black bars over Mann's daughter's eyes, nipples and vagina, as if the everyday nakedness of a four-year-old girl was a problem.
Mann defended herself, arguing that her work is "natural through the eyes of a mother, since she has seen her children in every state: happy, sad, playful, sick, bloodied, angry and even naked."
At the moment Sally Mann's photography is on display in her first solo exhibition in the UK, The Family and the Land, at the Photographers' Gallery in London. With a bit of distance, and in the context of a large body of work, it is a good time to revisit the series.
The black-and-white pictures of Mann's children were taken over a 10-year period on a large-format 8x10-inch camera, around her home in the woods and lakes of Virginia. Her subjects are far from comfortable.
Jessie, Virginia and Emmett stare right into the lens. They look like children but appear to pose in an adult way; with a cigarette, or wearing pearls and little else, or dancing with no clothes on. One is titled, almost angrily, The Last Time Emmett Modeled Nude.
Many are disturbing. In The Terrible Picture, one of her daughters appears to hang dead from a tree. Others are beautiful, like Virginia at 6, where the little girl stretches her arms up, body arched like fish, naked next to a lake, her wet hair stuck to her back echoing the ripples of the water.
Yes, a few challenge conventional ideals of childhood. But they are also ordinary and document recognisable, intimate moments. We have all seen the future adult in the child, the wavering between youth and maturity and the physical beauty of the young. There is nothing untoward here.
Mann's other work on show is also intense. The more recent series, What Remains, examines how bodies, as they decompose, merge into the land. They are strong pieces, but interestingly enough, the photographs of the dead rotting corpses have provoked little comment. Not so the photos of the recorded lives of her three little kids.
The trouble is that, because of the huge controversy, it has now become almost impossible to look at the artworks innocently, as depictions of childhood. You cannot help but ask, could they be seen as pornographic? And this pollutes our minds.
Unfortunately, this approach to images is encouraged, as Hadaway points out: "The child-protection regulations instruct us to put ourselves into the place of the paedophile when we look at images today. Thus we are no longer assessing the piece, or the subject, but instead how it could be interpreted." We need to stop thinking like a paedophile and retrain ourselves to see the innocence in images of children and enjoy them.
What is at stake here is not just free expression. Intense anxiety about how others might interpret actions and images means not only the effective censorship of artwork, but also, Sank warns, "it closes down our imagination and restricts how adults interact with children, which fills me with sadness as it makes us blind to the wonder of life and the wonder of people."
Some time after the furore, in an interview for Aperture magazine, Jessie, one of Mann's daughters, dismissed the controversy surrounding the notion of child exploitation as "puritanical idiocy". She asserted that "...despite the way those photographs complicated and expanded our lives, I believe that the entire process was for our own good, because it was done with faith in art."
All credit to the Photographers' Gallery for giving us a chance to try to restore that faith in Mann's work and each other.
Tiffany Jenkins is director of the arts and society programme at the Institute of Ideas. The Family and the Land is on until 19 September at the Photographers Gallery in London ( photonet.org.uk)