1. An image forming apparatus that forms an image on a recording medium, based on image signals on which add-on signals are added, the add-on signals being adapted to form add-on dots read by an analysis device that analyzes tracking information, comprising: a halftone processing section that converts an input image signal to a halftone processing image signal having a halftone processing cycle; a signal add-on section that adds the add-on signals on the halftone processing image signal; a control section that acquires position information to determine a relative position of an image formed according to the halftone processing image signal and add-on dots formed according to the add-on signals in a first image area among plural image areas defined in accordance with common multiples between a halftone processing cycle of the halftone processing image signal and a minimum interval among the add-on dots formed according to the add-on signals without overlapping the image formed according to the halftone processing image signal and the add-on dots formed according to the add-on signals, wherein the control section acquires other position information to determine a relative position of an image formed according to the halftone processing image signal and add-on dots formed according to the add-on signals in a second image area, based on the position information acquired in the first image area.