In the scan preview you can select a portion of the preview to saved as the final scan.
A dotted line box with eight small black boxes on the corners, and on the sides surrounds the area that is currently selected. Portions of the preview outside of the dotted lines will not be part of the final scan. This box can be manually resized by clicking and holding one of the eight smaller boxes, and then dragging to the desired size. After the area you wish is selected, click Accept.
Figure : Selecting the scan area