OMR (Optical Mark Recognition) marks are horizontal or vertical black solid lines found on printed mailing sheets. The mail processing machines check for these lines on every page fed in the system. The tracking of these marks triggers mechanical processes like the folding of all pages that should be inserted together in an envelope. The technology is also used for identifying marks such as crosses, donuts, etc. in scanned documents and is part of most current OCR / ICR engines. The typical use is in the automated collection of questionnaires or completed forms.