a first detector that detects products to be registered when the products enter an upstream process of a plurality of processes constituting a production line for products, the first detector detecting the products as the products individually enter the upstream process;

a second detector that detects the products when the products enter a downstream process of the plurality of processes, the downstream process being downstream from the upstream process, the second detector detecting the products as the products individually enter the downstream process;

a first memory containing program instruction; and

a processor coupled to the first memory, wherein the processor is configured to execute the program instructions to:

when the first detector detects a current upstream product of the products, acquire a captured upstream image of the detected current upstream product to be registered as a registration image, and store the registration image in a second memory in association with product information including information representing a passing sequence of the products through the upstream process;

manage a matching sequence of the products through the downstream process; and

when the second detector detects a current downstream product of the products, acquire a captured downstream image of the detected current downstream product, and perform matching between the captured downstream image and the registration image stored in the second memory for the current upstream product corresponding to the current downstream product, according to the matching sequence,

wherein management of the matching sequence includes, when the matching succeeds, updating the matching sequence to include just the registration image of each of the products that have not been matched with the captured downstream image, in an order corresponding to the products in the passing sequence.