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Title: Cornell Researchers Develop Invisible Light-Based Watermark To Detect
Deepfakes

Link: https://slashdot.org/story/25/08/12/2214243/c...

Cornell University researchers have developed an "invisible" light-based
watermarking system that embeds unique codes into the physical light that
illuminates the subject during recording, allowing any camera to capture
authentication data without special hardware. By comparing these coded light
patterns against recorded footage, analysts can spot deepfake manipulations,
offering a more resilient verification method than traditional file-based
watermarks. TechSpot reports: Programmable light sources such as computer
monitors, studio lighting, or certain LED fixtures can be embedded with coded
brightness patterns using software alone. Standard non-programmable lamps can
be adapted by fitting them with a compact chip -- roughly the size of a
postage stamp -- that subtly fluctuates light intensity according to a secret
code. The embedded code consists of tiny variations in lighting frequency and
brightness that are imperceptible to the naked eye. Michael explained that
these fluctuations are designed based on human visual perception research.
Each light's unique code effectively produces a low-resolution, time-stamped
record of the scene under slightly different lighting conditions. [Abe Davis,
an assistant professor] refers to these as code videos. "When someone
manipulates a video, the manipulated parts start to contradict what we see in
these code videos," Davis said. "And if someone tries to generate fake video
with AI, the resulting code videos just look like random variations." By
comparing the coded patterns against the suspect footage, analysts can detect
missing sequences, inserted objects, or altered scenes. For example, content
removed from an interview would appear as visual gaps in the recovered code
video, while fabricated elements would often show up as solid black areas.
The researchers have demonstrated the use of up to three independent lighting
codes within the same scene. This layering increases the complexity of the
watermark and raises the difficulty for potential forgers, who would have to
replicate multiple synchronized code videos that all match the visible
footage. The concept is called noise-coded illumination and was presented on
August 10 at SIGGRAPH 2025 in Vancouver, British Columbia.

Read more of this story at Slashdot.

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