A victims' charity has said it is "astonished" artwork by notorious British criminal Charles Bronson has been put on display on the Tube.
The drawing, which depicts a head with three faces poking out of a straitjacket, went on display at Angel station in north London on Monday.
Benjamin Moore, from Art Below, which displays art on the Tube, said the artwork was "unique".
The National Victims' Association said it was "depressed" the work was put up.
A Transport for London (TfL) spokesperson said: "Art Below is not part of the Art on the Underground, the Tube's official arts programme."
Bronson, 58, was jailed for armed robbery in 1974.
He has committed a string of crimes behind bars, including hostage-taking, and rooftop protests and has spent much of his time in jail in solitary confinement.
Mr Moore came into contact with Bronson through mutual friend Tom Hardy, who played the criminal in the 2009 film Bronson, which is based loosely on the prisoner's life.
He received a letter from Bronson saying he would like his work displayed on the network.
The artwork, which will be displayed at the station for two weeks, is one of about 60 pieces by Bronson that Mr Moore says he saw and was among only a few that made it through copy approval by TfL.
"There's a lot of madness and sadness in his work but what struck me was the humour," Mr Moore said.
He says he thinks Bronson's artwork is unique because of the amount of time he has spent in confinement.
"You'll never see any artwork like it because no artist is going to spend more than 36 years inside an incarcerated space."
But the National Victims' Association (NVA), which supports victims and families affected by crime, criticised the move.
"I would say that the overwhelming majority of victims of crime will be astonished and thoroughly depressed that one of the most violent criminals in the prison system is allowed to engage with the British public in this way," a NVA spokesman said.
"There will be many members of the public who will find it deeply disturbing to be confronted by someone whose behaviour towards society is so dastardly."
Mr Moore said that the art "comes from a place no one else will ever reach. In that sense it's quite dark. He's lived inside his mind for all that time."
"His art and his physical training are the two things that have helped him survive mentally this long."
The prisoner is said to have developed an extreme fitness regime while in prison and has had a book published, advising how to exercise with minimal resources and space.
TfL said: "The artwork was submitted by an organisation called Art Below via CBS Outdoor who manage advertising space on the Tube network.
"The companies who manage advertising on behalf of TfL assess all adverts submitted for display on London's transport network to ensure compliance with TfL's advertising guidelines".
Bronson, born Michael Peterson in Luton, Bedfordshire, changed his name in the 1980s in homage to the star of the Death Wish films.