Lines and streaks on scanned documents

Vertical lines down every page are the most common image problem on document scanners, and they are almost always dirt, not a fault. In a sheet-fed scanner the sensor stays still while the paper moves past it, so one speck of dust, glue or correction fluid on the glass draws a line the full length of every page. On a flatbed, where the sensor moves, the same speck makes only a spot.

Fix it in this order

• Clean the scanning glass. Open the feeder and wipe the glass strips with a lint-free cloth and the cleaner your scanner's maker recommends. Duplex scanners have two glass strips, one for each side of the page, and a line on only the back of each page points to the second one.
• Look for residue such as correction fluid, label adhesive or toner, which may need a few passes. Spray cleaner onto the cloth, never onto the scanner.
• Clean the rollers too. Dirty rollers spread residue back onto the glass. See cleaning kits and cleaning sheets.
• Run the scanner's calibration, if it has one. Faint colored lines or uneven brightness across the page often clear after a shading calibration, which some models do with a supplied calibration sheet.

When cleaning doesn't fix it

• A sharp line that won't wipe off is usually a scratch in the glass. Scratched glass is replaced as a part; see scanner glass.
• Dark, dim or uneven images on an older scanner can mean a worn lamp; see scanner lamps.
• Stretched, squashed or banded images usually come from rollers slipping, not from the sensor; see double feeds and paper jams.

Some scanner drivers have a streak-reduction setting that hides thin lines. It is useful to keep a batch moving, but clean the glass anyway, because it can also remove fine lines that belong on the page.

Related

CCD and CIS image sensors  -  Scanner repair  -  The parts of a document scanner