What is the origin of the fake pornographic images of popstar Taylor Swift, which flooded the social network X for several days and sparked mass outrage last week? To answer this question we need to delve into some of the darker corners of the internet, into online communities that are usually kept well out of sight and away from the main mainstream social networks.

Late last week, US media identified the first culprit as a large discussion group on Telegram, a messaging app notorious for its almost total lack of moderation. In this forum, journalists from the industry website 404 Media discovered posts of some of the deepfakes before they appeared on X.

However, according to an investigation by Le Monde, a large portion of the images that have been circulated in recent days originated from the message board 4chan, one of the internet's most unrestrained forums and infamous for its extreme content. Some of the most recent deepfakes had already been posted there in November and December.

For several months now, 4chan's "ACO" ("Adult cartoons") board has been featuring a long daily thread in which users post fake pornographic images of celebrities, made using automatic generation tools. This board, which used to be dedicated to pornographic cartoons, now also includes the images created by artificial intelligence (AI)-based software.

On some days, over a hundred new photo-realistic creations are posted on the forum. Swift is by no means the only victim of these deepfakes, but America's most famous popstar appears frequently in pornographic images that range from "soft" eroticism to extremely "hardcore" images.

Here, the creators also share their favorite tools, as well as tips and tricks for getting around the restrictions on commercial tools that prohibit pornographic images or the use of images of famous people. They also sometimes trade "prompts," the sequence of keywords used as instructions to generate an image, so that other users can adapt them as they please.

Faked pornographic images, such as those of Swift, have their own viral circuits, usually outside the major social networks. It's not uncommon, for example, for an image originally published on 4chan, because it's deemed particularly successful, to be widely reposted in Telegram groups - some, spotted by Le Monde, have over 100,000 subscribers - and on pornographic sites totally or partly dedicated to this type of image, with some even mimicking Instagram's layout.

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