3 min read
What our nudity detection sees, and what it misses
Unwanted nudity is the main reason people give up on random video chat. The reputation was earned.
Stranger checks video for nudity automatically. Below is how that works, step by step, including the cases it gets wrong.
How a frame is rated
Video on Stranger is relayed through our server. Every two seconds the server asks for a keyframe from the lowest-resolution layer of each person's stream. That picture is small. It is still more than enough to recognise nudity, and cheap enough to check for everyone at once.
An image classifier then scores the frame. We use an open-source Vision Transformer, Falconsai/nsfw_image_detection, trained to tell safe images from explicit ones. It returns a probability in well under a second, and from 70% the frame is treated as nude.
The model runs inside our own server process. Frames are not uploaded to an outside AI provider.
Three ratings: unrated, clean, nude
At any moment a video has one of three ratings. It is unrated until a usable frame has been checked, which is usually the case in the first seconds of a call. It is clean when the latest check found nothing. It is nude when a frame was flagged.
Getting back from nude to clean takes two clean checks in a row. One lucky frame is not enough to undo a flag.
What changes for you
The 18+ switch beside the video decides whether any of this affects your screen. It starts on, and with 18+ on nothing is blurred and you may be matched with people showing nudity.
Turn it off and two things change. A match's video stays blurred unless it is rated clean. And you are only matched with people who have already been rated clean, so the first match can take a few seconds longer.
When you are the one flagged
Your own video is rated as well. With 18+ off, a nude rating blurs your preview and your match's video, so you see it straight away.
Show nudity to someone who has 18+ off and a 15-second countdown appears. If your video is rated clean again before it runs out, nothing more happens. If not, the conversation ends and you are matched with someone else.
Where it falls short
Automated detection cuts down unwanted nudity. It does not remove it.
Two seconds is a long time on camera, and something shown briefly between checks can be missed. The model also errs in both directions: swimwear or a shirtless match can be flagged, while low light, an odd angle or a partial view can pass as clean. It only looks at video, so text messages and audio are not analysed at all. And it does nothing against screen recording; a match can still capture what you show. Our safety page covers that.
People make the final call
The detector can blur a video and end a conversation. It cannot ban anyone.
Bans are decided by moderators, who review reports and recordings and can watch conversations live. Recordings keep the original, unblurred video, so a decision rests on what actually happened. They are deleted after 30 days, as described on the privacy page. If something gets past the detector, report it and include the date and time of the conversation.
Why it is built this way
Checking every video on our own hardware, with people reviewing what the model flags, is the best balance we have found between safety and privacy that does not involve asking anyone for ID. To see it in practice, switch 18+ off and start a conversation.
