An automated monitoring service downloads image files (including, e.g, graphic and video files) and audio files from various Internet sites, and checks these files for the presence of embedded digital watermark data. When found, such data is decoded and used to identify the proprietor of each watermarked file. The proprietors are alerted to the results of the monitoring operation, often apprising such proprietors of unknown distribution of their image/video/audio properties. Digital watermarks carry control flags used to control viewing or playback depending on content classification.