1. A document scanner comprising: an input tray for holding documents; an input image capture device for capturing at least a portion of images of documents in the input tray; an image processor for determining characteristics of documents in the input tray; wherein said documents are processed based on said characteristics; wherein at least one characteristic is document length or width or position or other characteristics; ultrasonic zone for detecting the documents; and wherein the ultrasonic zones are enabled or disabled in at least one location down the document based on the at least one characteristic.