1. A method comprising: receiving imagery representing two packaged items from a digital camera, each of the packaged items including digital watermarking encoded in packaging on the items; using one or more programmed electronic processors, analyzing the imagery to detect the digital watermarking; accessing a spatial template associated with the digital watermarking when two or more instances of digital watermarking are detected in a single image frame; comparing spatial areas containing the two or more instances of digital watermarking within the imagery to the spatial template; carrying out an action based on said comparing.