Forensic Watermarks in Mobile Devices

Researchers are working on a new watermarking scheme to deter people from illegally sharing videos.

As video content shows up on more and more cell phones, content providers are looking for new ways to curb illegal distribution. Researchers at Cinea, a subsidiary of Dolby, are working on a system that embeds a unique digital signature called a forensic watermark into a video after it's downloaded. The watermark, explains Robert Schumann, general manager of Cinea and board member of the Digital Watermarking Alliance, contains bits of data, hidden from view, that allow content providers to trace a video back to the phone or device on which it was downloaded. The goals, he says, are to deter people from widely distributing a downloaded video and to have a method of finding individuals who illegally share video.

Yellow and magenta boxes highlight the location of imperceptible changes in pixels that make up a forensic digital watermark in a single video frame. Credit: Cinea Inc.

The most common way to deter illegal distribution of music and movies is through digital rights management technology (DRM): instructions embedded in the files that limit their use. For instance, music bought from Apple's iTunes music store uses the DRM scheme called FairPlay, which allows songs to be played only on an Apple iPod MP3 player and a limited number of authorized computers.

Schumann says watermarking technology could offer a less restrictive alternative to DRM. "People are not happy with how DRM works today," he says. The limits imposed by DRM are not necessarily because content owners don't want an individual to make five or six copies of a CD, he says, but because content owners are looking for a way to keep people from making one million copies. Watermarking, Schumann says, could potentially give people more freedom than some current DRM schemes, allowing consumers to shuttle video or music from device to device, and to share copies with friends. "If you use the video [on your own electronic devices], then nobody knows the [watermark] is there," he says. "But if we find a million copies of [the video containing your unique watermark] out on the Internet, then we might come looking for you."

Embedding a forensic watermark is typically a computationally intense task. Pixels of the video need to be altered to create the watermark, and ideally, those alterations are invisible. Each scene must be analyzed to determine which pixels to alter. Cinea wants to create a system that can embed these watermarks using the limited processing power of devices such as mobile phones.