The social network is making it impossible to repost or share intimate images of people thought to have been uploaded without their permission once they have been identified as such and removed.

The measure is being rolled out across Facebook, Messenger and Instagram but not WhatsApp.

Campaigners welcomed the development.

"It's a huge step forward," said Laura Higgins, founder of the UK's Revenge Porn Helpline.

"Quite often these images are posted on social media as part of a domestic situation in which someone is trying to get at their target and their nearest and dearest.

"One of the greatest challenges is to stop people re-uploading the content."

'First step'

Facebook is not hunting out revenge porn imagery itself, but instead will rely on users flagging the content via its Report tool.

Its community operations team will then make a judgement as to whether the posts qualify, taking into account factors including whether sexual activity is depicted, the setting and whether the person making the complaint is shown.

If the image is judged to be revenge porn, it will be removed and the account that posted it blocked, pending a potential appeal.

Photo-recognition software is then deployed to ensure any further attempts to circulate the picture are blocked without human operators needing to review them.

The technique is similar to that already used by Facebook and others to prevent child abuse imagery being shared.

"We are constantly looking to build and improve the tools that we offer and it became very apparent to us that this was a problem occurring across many regions that created unique harm," Antigone Davis, Facebook's global head of safety, told the BBC.

"This is a first step and we will be looking to build on the technology to see if we can prevent the initial share of the content."

Ms Davis added that Facebook might look at how it could tackle the problem on WhatsApp in the future.

However, the app's use of end-to-end encryption prevents Facebook from being able to see what users are sending to each other.

Devastating attack

Ms Higgins said her organisation had dealt with more than 6,200 cases of revenge porn since 2015 - a figure she called the "tip of the iceberg".

"Our clients have presented with post-traumatic stress disorder, suicidal feelings - they can lose their jobs, marriages and children," she said.

"It's an absolutely devastating thing to have done to you."

She said that dedicated revenge porn websites remained the biggest problem, but added that she hoped other social media companies might follow Facebook's lead.