Pakistani police are investigating the so-called “honour killing” of a young woman who appeared in a viral photo that police suspect was doctored.

Authorities in remote Kohistan said the 18-year-old was shot dead by her father and uncle last week on orders from elders of a tribal jirga (council).

Her father was arrested on a murder complaint and her uncle is on the run, police say. She has not been named.

The man in the photo, whom the jirga wanted dead, is in protective custody.

Two others – a young woman and a young man – also received death threats after their doctored pictures went viral on Pakistani social media, police said.

Police said the pictures in both cases appeared to have been photoshopped and posted on fake social media accounts, and that they are investigating who is behind the pictures.

Local authorities took the second woman into protective custody but released her back to her family after a court hearing, where she said she faced no risk to her life at home.

Kohistan, a mountainous region of northern Khyber Pakhtunkhwa province, is a notoriously conservative and inaccessible area where a number of so-called honour killings have been reported in recent years. These killings are usually carried out by relatives who say they are acting in defence of their family’s honour.

On Monday, Pakistani media outlet Geo News reported police were also raiding the home of the dead woman to find other villagers involved in the call for her killing.

In areas such as Kohistan, the idea that a murder can be “honourable” is believed to have come from tribal customs, where an allegation against a woman is perceived to have brought dishonour upon relatives. According to these customs, male family members of a woman who has interactions with unrelated men – however innocuous – should first kill the woman, then go after the man.

Human rights groups say the most common reasons for “honour killings” are that the victim may have refused to enter into an arranged marriage or have been raped or sexually assaulted.

But killings can be carried out for more trivial reasons, like dressing in a way deemed inappropriate or displaying behaviour seen as disobedient.

In Pakistan, hundreds of women are killed in this way each year. A much smaller number of men are murdered in such cases.

The murders shocked the country and led to calls for stronger law enforcement and actions to stamp out so-called honour killings.

In 2016, Pakistan’s government amended legislation so that killers would get a mandatory life sentence. Previously, they could avoid a jail term if pardoned by the victim’s family.

Despite the change in the law, killers are still evading justice, human rights groups say.

Last year the brother of social media star Qandeel Baloch was acquitted of murdering her on appeal. He had been sentenced to life in prison after confessing to the 2016 killing, saying it was because the star had brought shame on the family.