The present invention provides a sheet for forming an image having an identifying mark, an image forming method, and an image forming apparatus using the same, wherein the identifying mark is useful to identify various information concerning the sheet. The sheet for forming an image is provided with two or more image-formative layers which are defined by frame respectively and arranged in a longitudinal direction of the sheet. The identifying mark comprises a sequence of mark bits which records the information, and the mark bits are respectively allocated to unit frames each of which comprises a single frame or plural frames of the image-formative layer with the mark bits being arranged in order of the sequence recording the information and repeated at least one cycle period of a certain number of the unit frames along with a longitudinal direction of the sheet for forming an image, wherein the sequence of the mark bits constituting the identifying mark is a combination of a sequence of mark bits constituting a first mark A with a sequence of mark bits constituting a second mark B, the first mark A having a cycle period of a natural number X, the second mark B having a cycle period same as said X or of a natural number Y different from said X and relatively prime with said X.