1. An apparatus comprising: a print controller that causes a printing unit to print at least a first image part and a second image part on a first sheet, wherein the first image part includes two parts, one part of which includes clusters of dots and the other part of which includes dots, and the clusters are provided more sparsely in the one part than the dots are provided in the other part, and the second image part includes two parts, one part of which includes clusters of dots and the other part of which includes dots, and the clusters are provided more sparsely in the one part than the dots are provided in the other part, wherein a density difference between the one part and the other part in the first image part printed on the first sheet is different from a density difference between the one part and the other part in the second image part printed on the first sheet; and a user interface that receives, from a user, identification information identifying one of the first image part and the second image part printed on the first sheet, wherein the print controller is configured to cause, in accordance with a print instruction given after the reception of the identification information, the printing unit to print, on a second sheet, an image obtained by combining image data which is based on the received identification information and other image data, wherein a part of the image printed on the second sheet that corresponds to the image data which is based on the received identification information includes two parts, one part of which includes clusters of dots and the other part of which includes dots, and the clusters are provided more sparsely in the one part than the dots are provided in the other part, wherein densities of the one part and the other part in the part of the image printed on the second sheet correspond, respectively, to densities of the one part and the other part of the one of the first image part and the second image part printed on the first sheet that is associated with the received identification information and wherein the density of the one part in the part of the image printed on the second sheet is dependent on a number of the clusters per unit area and a size of the clusters in the one part in the part, the density of the other part in the part of the image printed on the second sheet is dependent on a number of dots per unit area and a size of the dots in the other part in the part, the density of the one part of the one of the first image and the second image printed on the first sheet that is associated with the received identification information is dependent on a number of the clusters per unit area and a size of the clusters in the one part of the one of the first image and the second image printed on the first sheet, and the density of the other part of the one of the first image and the second image printed on the first sheet that is associated with the received identification information is dependent on a number of dots per unit area and a size of the dots in the other part of the one of the first image and the second image printed on the first sheet.