If part of the document extends beyond the document table, that edge may not be in contact with the document table. Change the position of the document.
The image is faint or out of focus.
Check that the document is placed flush against the document table.
Check the Gamma setting in your software.
Check the Exposure setting in your software.
The image is too dark.
Adjust the brightness with your software. Also check the brightness and contrast values of your display screen.
Straight lines in the image are jagged.
The document may be placed at an angle on the document table. Align it so that the horizontal and vertical lines are carefully aligned with the scales on the top and side of the document table.
The image does not look the same as the original.
Try different combinations of image settings using your scanner software.
Your software may not have sufficient color matching and color management features, or these components of your software may not be correctly installed. (See your software and computer manuals.)