When scanning an image using the <Auto Size> auto-acquire feature, extra space is being returned around the image.
Dust and scratches on the scanner flat bed are being misinterpreted by the software as being part of the image.
Reduce the AutoDetect sensitivity factor:
Select Tools > TWAIN Devices ... from the menu.
Double-click on the TWAIN device returning the extra space around the image.
Set the 'Sensitivity' to Normal Sensitivity.
Reduce the 'Sensitivity Factor' to the next level (typically, this factor should be set to Medium).