The present invention allows a thumbnail display representing the outline of input images in a digital image printer to be made, in which it is determined whether an image is a first kind of image or a second kind of image, and if it is determined that the image is the first kind of image, a feature part of the first kind of image is enlarged in the thumbnail display to make the contents of image more understandable.Also, the invention allows a thumbnail display representing the outline of input images in a digital image printer to be made, in which it is determined whether an image is a character image or a gradation image, and if it is determined that the image is the character image, a part of the character image is enlarged in the thumbnail display to make the characters more understandable.