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.