An image forming method includes marking a cutting pattern over an image to be printed, designating portions of the cutting pattern as a portion to be kept in the image to be printed and a portion to be discarded, creating an image mask using information of the designated portions, applying the image mask to create a modified image in which the portion to be kept is exposed and the portion to be discarded is hidden by the image mask, applying colorant only to the portion to be kept of the modified image, which is exposed by the image mask, to create an outputted image with colorant only on the portion to be kept, and cutting away the portion to be discarded of the modified image, which is hidden by the image mask, so that the portion to be discarded is not included in the outputted image.