1. A network system in which image data items are uploaded from a plurality of user terminals to a server and images are opened to public among the users, the system comprising: an uploaded image storage unit configured to store image data items uploaded from the terminals; a work storage unit configured to store a plurality of image data items stored in the uploaded image storage unit as works for publication; a classification unit configured to classify the plurality of works stored in the work storage unit into a plurality of categories; a display control unit configured to display the works for each of the categories on a display device of the terminal; a browse request unit configured to select a work from the terminal and make a browse request; a count unit configured to receive a browse request from the terminal and count the browse request number of times; and a category division unit configured to divide the works classified into the categories into a first group of works with each of which the counted browse request number of times is greater than or equal to a predetermined number, and a second group of works other than the works in the first group, and classify one of the first and second groups of the divided works as another category different from the categories.