A document scanner (10) includes an input tray (20) for holding documents; a transport system (45) for moving documents through the scanner; at least one document detection sensor (135A-135E) for detecting documents; an image capture device for capturing image data for a document; an image processor for determining characteristics of the document based on the image data; and wherein the processor compares characteristics of the document to ultrasonic data and excludes ultrasonic data which conflicts with image data.