A system that "watermarks" video electronically and tracks its use has been launched by New York-based Medialink Worldwide. The system can provide digital video monitoring and real-time broadcast tracking to the international broadcasting, programme syndication and advertising industries.

TeleTrax uses technology developed by Lucent, of the US, to stamp video footage invisibily and indelibly with an unique identifying code when it is produced, transmitted, duplicated or broadcast.

Receivers monitoring broadcast signals detect the code and relay information over the Internet to Medialink's computer centre.

Medialink sends the results, plus information identifying each station that broadcast or transmitted any portion of the encoded video and the date, time and duration of use, to clients via the Internet. Medialink (www.medialink.com) plans to build a monitoring network to ensure all TeleTrax-encoded broadcasts are detected.