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Screening - http://en.wikipedia.org/wiki/Screening_(printing) If the dots are visible to the naked eye then it gets tagged. If you are not 100% sure then tag it with 'scanning_artifacts' as well

Crease - A bend/crease in the scan.

Binding_discoloration - The scanner hasn't de-binded the artbook. If you can't lay the image perfectly flat on the scanner, you'll get discoloration of the scan.

IMO - the easiest scans to fix with processing are in this order - screening, crease, JPEG artifacts, binding discoloration, scanning artifacts, paper texture, bleed through, gap.

Anyone want to expand on this?