A device for recording data and data structures on a write-once storage medium. A digital image of an object substrate is attained through microscopic observation thereof, the attained digital image is examined to detect defects, while masking a region pre-registered in terms of coordinates, or while masking a pattern meeting a pre-registered pattern, and an image of each of the defects thus detected is displayed. The method also prevents unauthorized access, and facilitates authorized access, to computer networks.