Disclosed are a system and method for writing WORM data to a data storage device by use of a WORM LBA indicator. The method and the system decrease estimation errors due to height, thereby enabling common use by a number of nations each having a different average height, and decreasing cost of development and manufacturing. An image-processing unit, which is arranged inside the projector or an external electronic device, receives the human-shape image, creates a human-shape black mask, and outputs the human-shape black mask via the projector onto an area of the screen corresponding to the user’s position.