1. A method of managing media items in a media retrieval system based on episodic memory of a social group, comprising: when a user opens a new session with the retrieval system, authenticating the user as a member of a pre-registered social group, importing media items from the user, storing the media items in storage for subsequent viewing, tagging retrieval by members of the social group, determining whether the media items have been tagged with index information, the index information representing episodic memory triggers of the social group and including at least one valid selection taken from the group triggers of: persons associated with the social group, event types associated with the social group and time associated with the social group, and purging select media items from storage that remain untagged a predetermined amount of time after having been imported to the media retrieval system, wherein media items that are tagged within the predetermined amount of time are protected against the purging.