This happens when:

• The imaging lens may need to be cleaned.  
• Any ink or dust on the Imaging Lens will cause black lines on the scanned image.

Before cleaning the scanner, always disconnect the power and never use solvent or harsh chemicals to clean it as they may damage or discolor the scanner.

Please refer to the link:

• Cleaning Digital Check/Tellerscan

TellerScan TS240 Cleaning - YouTube

Digital Check Troubleshooting the TS215-TS230 by Cleaning the Scanheads - YouTube

• Cleaning RDM

Cleaning The Scanner; Cleaning The Outside Cabinetry; Cleaning The Inside Of The Scanner Unit; Cleaning The Image Sensor - RDM EC9100i series User Manual [Page 31] | ManualsLib

• Cleaning Panini

How to Clean a Panini Check Scanner with a Panini Check Scanner Cleaning Card - YouTube

Once done cleaning, run a test in OneSite.