1. A method comprising: in a network system, receiving items of content captured by electronic devices associated with users, the received items being uploaded to the network system, and the network system is configured to stream or download the received items to other users of the network system; with one or more processors, executing instructions to perform the acts of: extracting digital watermarks in audio signals from the received items of captured content; with watermark IDs decoded from the digital watermarks, querying a database to obtain a first instance of metadata associated with a first watermark ID extracted from a corresponding first instance of received item and querying the database to obtain other instances of metadata associated with other watermark IDs extracted from corresponding other instances of the received items; correlating the first instance of metadata associated with the first instance of received item with the other instances of metadata corresponding to the other instances of the received items, the correlating identifying related received items that have correlated metadata; and aggregating the related received items for presentation to a user of the network system.