1. An image processing apparatus for processing a plurality of document images contained in inputted image data, each of the plurality of document images containing an information image which provides a user with information, said image processing apparatus, comprising: a reliability determining section which determines, with respect to each of the plurality of document images, reliability of coincidences of respective predetermined directions with a first reference direction, the first reference direction being a predetermined direction which points on a basis of an upward direction of or a downward direction of the information image; and a display control section (i) which divides the plurality of document images into groups so that document images, having a same direction whose reliability value is the highest, belong to a same group, and (ii) which causes a display device to display preview images for the respective groups, each of the preview images indicating at least one document image in each of the groups.