A boy who killed his stepmother with an axe and samurai sword was "obsessed" with watching extreme violence.
Rueben Brathwaite, 17, admitted murdering Fiona Scourfield, 54, at Broadmoor Farm in Laugharne, Carmarthenshire, on 6 March.
Brathwaite was sentenced to life in prison at Swansea Crown Court, with a minimum of 15 years.
Judge Mr Justice Simon Picken said it was a "savage attack against a defenceless woman".
Brathwaite killed dog rescuer Ms Scourfield before trying to upload pictures of her body to the internet.
The court heard the teenager developed an interest in videos of beheading, suicide and mass murder on website 4chan in the run up to the murder.
Prosecutor Paul Hipkin said: "The images demonstrated murder, death and mutilation."
The court heard Brathwaite arrived home from a "normal school day" and later in the afternoon, he lured Ms Scourfield outside and repeatedly struck her over the head with an axe.
He then cut her throat with a samurai sword taken from underneath his father's bed.
Following the attack the teenager called the police, confessing to the murder.
Mr Hipkin said when officers asked why he had murdered Ms Scourfield, he said he was "fed up of life" and saw killing his stepmother as a "way out".
Brathwaite considered attacking his father but thought he would be "too powerful" and would fight back.
In the 999 call to police, he said: "I've just killed someone. The person is Fiona Scourfield.
"I know she's dead. Her pulse has stopped. There's no signs of life. I hit her so many times in the head, about eight to nine times with the axe."
He later told police his stepmother took good care of him and he was "sure she loves me and my father".
Paul Hobson, defending, said the violent content Brathwaite regularly watched in the months leading to the killing meant "after time, a natural revulsion to pain and crime became deadened to him".
After the attack, Brathwaite took two photos of the victim's body which he tried to upload to 4chan, but failed.
Mr Hobson said his client had "committed a dreadful crime" and Ms Scourfield's death was "brutal and served no purpose".
Brathwaite told the court: "I believe without the right level of help I believe I will remain a danger to myself."
In a letter to the court, Brathwaite said his stepmother was a "great believer in me" and wanted him to go to university, adding she had "so much love for me".
Ms Scourfield was described as "loving and caring" by family and volunteered with the German Shepherd Rescue UK charity.
Mr Justice Picken said Brathwaite complained of loneliness, unhappiness and depression but had not been suffering from any mental health condition.
He added: "No doubt inspired by the graphic images seen on the internet in the months before the attack, you attempted to upload images of the attack to the internet.
"Your obsession went to watching material including mass murders and massacres."
A victim impact statement read on behalf of Ms Scourfield's mother Charlotte said: "Fiona made Rueben warmly welcome and made sure he was properly dressed and equipped for school.
"I believe there was a loving bond between them. My life is destroyed."
After the hearing, Det Supt Gary Phillips from Dyfed-Powys Police said Ms Scourfield "lost her life in a savage and unprovoked attack".