1. An image processing apparatus for outputting an index print of information representing a plurality of images, comprising: input means for inputting the plurality of images to which numbers are respectively assigned according to a numerical order; means for detecting size information for each of the plurality of images based on respective image size; decision means for determining an outputting order, which is different from the assigned numerical order, according to the detected size information for each of the plurality of images; and output means for outputting the plurality of images according to the determined outputting order.