1. An image display controlling apparatus, comprising: image-data maintaining means for maintaining a plurality of image data; link management means for managing a link representing a parent-child relationship of parent image data and child image data between two image data in the plurality of image data; operation receiving means for receiving operation input relating to a display of the plurality of image data; and display controlling means for controlling such that switching is performed between a whole display in which all of the plurality of image data is subject to be displayed and a digest display in which image data other than those which are the child image data by the link, out of the plurality of image data, are subject to be displayed in response to the operation input.