A vertical black line that appears only in an automatic document feeder scan can come from debris on its narrow scanner glass. Compare the feeder and flatbed paths before painting out the line in every file. For valuable or fragile old photographs, use an appropriate flatbed or specialist capture route; test the feeder with an ordinary permitted paper copy instead.
Identify which path creates the line
Brother's linked troubleshooting article separates printing, flatbed copying and feeder copying. Its listed products include DCP-L2550DW and DCP-L2640DW. That scope matters: the glass location and cleaning materials in this answer should not be treated as instructions for every scanner sold under the brand.
Start with a plain test sheet that the machine permits in its feeder. Check the sheet itself, a saved flatbed scan and a saved feeder scan at the same useful magnification. Keep the scanning settings and orientation recorded. If the defect appears in a printed copy, also distinguish a printing defect from one already present in the digital scan.
Clean the relevant scanning surface
A small stationary obstruction can become a continuous line as paper moves past the scanner. In the referenced Brother procedure, the narrow glass strip and adjacent white pressure bar are specific cleaning targets. The instructions call for lightly moistening the cleaning cloth, rather than spraying the machine directly.
Confirm that the procedure covers your actual model before using its cleaning agent or cloth guidance. Cleaning the broad flatbed glass while missing the feeder strip does not test the proposed cause. Conversely, if both paths produce the line, do not continue assuming that only the feeder surface is involved.
Compare an ordinary paper test before and after
This is a reproducible test plan, not a completed scanner repair. Save the first pair of digital scans under distinct names. Perform the applicable documented cleaning and allow the machine to be ready for use. Scan the same permitted paper sheet again, preserving its settings and placement as closely as the two paths allow.
Compare the line's position, width and continuity, as well as nearby text strokes. A lighter line is not the same as a clean capture. Keep the pre-cleaning file to show what changed. If a line remains after the documented maintenance route, use the model's support process rather than repeatedly rubbing an unidentified component.
For a hypothetical family album project, this paper comparison diagnoses the equipment while the original photograph stays outside the feeder. After resolving the capture condition, acquire the original through a suitable path. This example has not been executed and does not certify a particular machine's restoration performance.
Accept clean capture before image restoration
Accept the acquisition when the saved scan has no added vertical line and fine original strokes remain intact. Record the scanner, capture path and settings with the accepted file. Do not discard genuine marks in the original by interpreting every dark feature as a scanning defect.
Imagild can help prepare an artistic or restored photo treatment from a suitable input. It does not clean feeder glass or establish that a physical original is safe to feed. Keep equipment diagnosis and the later image edit traceable so that recurring acquisition errors do not become repeated retouching work.