DIGITAL watermarks built into movies now make it possible to identify the seat a video pirate was sitting in when they made an illegal camcorder copy.
鈥淎udio watermarks tell you how far the pirate is from the cinema鈥檚 speakers, even identifying the seat鈥�
Cheap copies of major movies such as Slumdog Millionaire (pictured) hit the streets as soon as the film is out. But now Noboru Babaguchi of Osaka University in Japan and colleagues claim that if you know which cinema a pirate operates from, you can locate where they were sitting by adding an audio watermark into the movie鈥檚 soundtrack. This is introduced during the mixing of the soundtrack by slightly varying the waveform of music and speech at regular intervals.
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Babaguchi created an audio watermark with a specific signal for each separate 鈥渃hannel鈥� of a soundtrack, broadcast from different loudspeakers in the cinema. By analysing the recorded audio from a camcorder copy, the team worked out how far away the camera鈥檚 microphone was from each of the loudspeakers, pinning it down to a specific seat. 鈥淭his is a brand new application of the digital watermarking technique,鈥� they write in a paper to be published in IEEE Transactions on Multimedia .
But the only way to identify the culprit would be to photograph ticket buyers, something which could create privacy problems in many countries, says Stephen Jenner of the in Sydney, Australia.
