TikTok’s parent company ByteDance has built technology to let users insert their face into videos starring someone else, TechCrunch reports.

The unreleased feature uses Deepfake-style technology referred to as ‘Face Swap’ by the app’s code. The code appears in both TikTok and its Chinese sister app Douyin, and invites asks users to take a multi-angle biometric scan of their face, then choose from a selection of videos they want to add their face to and share. The app verifies that the user is a live human by asking them to blink, nod, and open and close their mouth.

The user can then choose from a selection of videos that ByteDance claims to have the rights to use to replace the face of whoever in the video with that of the user. The video can then be shared, though only with an overlayed watermark the company claims will help distinguish the content as not being real.

TechCrunch was tipped off about the feature by Israeli in-app market research startup Watchful.ai, which discovered the code in the latest version of TikTok’s and Douyin’s Android apps. While the feature is not available to users of either app, Watchful.ai was able to activate the code in Douyin to generate screenshots of it.

A TikTok spokesperson told TechCrunch that “…this is definitely not a function in TikTok, nor do we have any intention of introducing it. I think what you may be looking at is something slated for Douyin – your email includes screenshots that would be from Douyin, and a privacy policy that mentions Douyin. That said, we don’t work on Douyin here at TikTok.”

A Douyin spokesperson denied that the Face Swap terms of service appear in TikTok despite TechCrunch reviewing code from the app showing those terms of service and the feature’s functionality.

While the idea of building deepfake tech into such a popular app – the two have been downloaded 1.5bn times in total – may seem inadvisable, some might argue that it could raise awareness of the tech and make the app’s users more wary of believing everything they see and hear when the watch videos online.