The most popular is PDF-417, developed by Symbol Technologies. A term used to mean black and white images with no grayscale. Traditionally the main way to capture and store images of documents in document management systems. Collecting multiple pages together and separating with batch separators. Recently there has been some interest in using color coded bars scanned with a color scanner to identify batches.
Flatbed scanners damage the spline and provide a fuzzy image at the edges.
Carbonless paper can often produce a very faint image. New color scanners often include the ability to remove, or drop-out specific colors. Users want to drop-out background colors in order to capture the foreground information so as to apply OCR or some other recognition to it. Also provides a method to find specific pages. The image can sometimes be reconstructed electronically.