1. An image register apparatus comprising: a first holding unit configured to hold, in association with each other, local feature amounts of an image and information that specifies the image including the local feature amounts; a second holding unit configured to hold, in association with each other, information that specifies a registered image whose local feature amounts are held by said first holding unit and information that specifies a similar image similar to a partial region of the registered image; a searching unit configured to search registered images for an image partially similar to an input target image to be registered; and a register unit configured to, when a search result image obtained by the search of said searching unit includes the target image to be registered, exclude the target image to be registered from a holding target of said first holding unit, and register, in association with each other, information that specifies the search result image in said second holding unit and information that specifies the target image to be registered.