1. An image forming method for packing a plurality of image prints in a bag as finished prints corresponding to an order and outputting the bag containing the plurality of image prints, comprising: an image print producing step of recording each of the plurality of images on a recording medium based on image data which is reproduced corresponding to each of the plurality of images, thereby to produce the image prints on an image-by-image basis; a step of judging whether the bag needs to be sealed or not when the plurality of image prints thus produced are packed in the bag as the finished prints corresponding to the order; and an image print outputting step of packing the plurality of image prints in the bag as the finished prints corresponding to the order and sealing the bag containing the plurality of image prints based on a result of the judging, thereby to output the plurality of image prints contained in the sealed bag.