1. A content delivery system comprising: a registration module configured to identify a registration type for calibrating a current location of a device; a tracker module, coupled to the registration module, configured to track a subject of interest based on a context; a source module, coupled to the tracker module, configured to determine an information source based on the registration type; and a content module, coupled to the source module, configured to generate an overlay content based on the information source for displaying the overlay content for the subject of interest on the device.