1. An image processing apparatus comprising: an acquisition unit configured to acquire a read image which has been obtained by reading at least one original by a reading apparatus and includes an original region corresponding to each of the at least one original; a specifying unit configured to specify an object corresponding to contents of the original in the read image based on a group of pixels corresponding to luminance values smaller than a predetermined luminance value in the read image acquired by said acquisition unit; and a decision unit configured to decide a candidate region corresponding to each of the at least one original region by determining, in a case where said specifying unit specifies a plurality of objects, whether the plurality of objects are included in one original region.