1. An article estimating system configured to be able to acquire identification information for identifying an article and additional information for the article from a storage which stores the identification information and the additional information in association with each other for each of a plurality of articles each having a cover and a spine, the article estimating system comprising: at least one memory operable to store program code; at least one processor operable to read said program code and operate as instructed by said program code, said program code including: image acquisition code which acquires an image including the plurality of articles; extraction code which extracts, for each article, an image area showing the article from the acquired image; analysis code which analyzes the plurality of extracted image areas to acquire analysis information; first estimating code which attempts a process of narrowing down candidates of identification information estimated to correspond to the article in the image area among identification information of the plurality of articles stored in the storage to a predetermined number or less based on the acquired analysis information, for each of the plurality of image areas; information acquisition code which acquires additional information for the articles of the candidates from the storage as additional information of at least one reference article when candidates were able to be narrowed down to a predetermined number or less for the at least one image area by the first estimating code; and second estimating code which attempts the process of narrowing down candidates of the estimated identification information to a predetermined number or less, based on the additional information of the at least one reference article in addition to the analysis information when the additional information of the at least one reference article was acquired, for the image area including a spine, which is an image area in which candidates were unable to be further narrowed down to a predetermined number or less based on the analysis information by the first estimating code.