1. An image processing system that comprises an image processing apparatus and a work management apparatus, said work management apparatus comprising a management unit that manages a document identifier used to identify a document and a user identifier used to identify a user in association with each other; and said image processing apparatus comprising a reading unit that reads a document to generate digital data, a first specifying unit that specifies a document identifier of the document read by said reading unit, an authentication unit that authenticates a user, a second specifying unit that specifies a user identifier of the user authenticated by said authentication unit, and a registration unit that registers the digital data generated by said reading unit, when said management unit manages the document identifier specified by said first specifying unit and the user identifier specified by said second specifying unit in association with each other.