1. A method for achieving boundary localization during scanning, wherein, said method comprises: a regular ribbon, a sensor module capable of detecting the ribbon, and the file to be scanned is placed between the ribbon and the sensor module; said sensor module first scans the ribbon information and stores it in the storage module of the scanning apparatus; said file to be scanned is placed between the sensor module and the ribbon, the sensor is capable of deriving the boundary position of the file to be scanned by means of contrast measurement through the measured ribbon portion covered by the file to be scanned.