Watermarking of a motion picture release print (12) occurs by providing on at least one soundtrack (16) at least one tone of a particular frequency on at least one location unique to the release print. Typically, placement of the particular frequency tone occurs on locat ion(s) where the tone will have minimal impact on the existing soundtrack audio. A record of location(s) at which the particular frequency tone appears on the release print is maintained to facilitate comparison with the tones detected in audio visual work to determine whether the audio of an illegal media was recorded from that release print.