Using GIMP: Correcting and Touching Up Your Images - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 110

Most scan programs provide the following options:
• Number of colors to be scanned, i.e., color depth (black and white,
grayscale, color).
• Original document type, such as text, image, or ilm. Some scanners
come with an add-on device that allows scanning of photo negatives
and slides.
• Scanning resolution (usually selectable in predeined values, given in dpi).
• Furthermore, you normally ind two buttons:
• A Preview button that activates a low-resolution preview scan
• A Scan button that starts the scanning process
Figure 2.39
Scan program dialog
Insert your original document in the scanner. If you click the Preview
button, the image will be quickly scanned and displayed in the preview
window. The scan software will automatically identify the image margins and
mark them with a dashed line that is sometimes referred to as the selection
frame or marquee. You can resize the selection frame by hovering the mouse
above it and then clicking and dragging the dotted line until you've selected
the area of the image you want to scan.