1. An interaction control system, comprising: a light source module, projecting a pattern to a detection region; an image capturing device, capturing images of the detection region and generating image information stream based on the images; and an processor, coupled to the image capturing device for obtaining a subtracted image information by subtracting the currently captured image information to a background image information of the detection region so as to determine whether or not an object appearing in the detection region, when the object appears in the detection region, calculating a motion of the object based on a variation of the pattern imaged on a surface of the object toward the light source module, and generating corresponding control instruction to a host apparatus.