Printers / multifunction devices
Many office archives were not scanned from originals. They were scanned from copies of copies, or from pages printed by aging laser printers. Those marks follow the document into the digital file.
Common marks
| Symptom | Likely source | Digitization effect |
|---|---|---|
| Even gray fog across the page | Worn copier drum or overexposed copy | OCR loses punctuation and light type. |
| Repeated specks every few inches | Roller contamination | Software may read specks as periods, colons, or decimal points. |
| One pale vertical band | Low toner or dirty laser window | Letters disappear in a column, especially thin sans-serif fonts. |
| Dark edge shadow | Book or stapled packet not flat on glass | Deskewing may tilt a correct page to match the shadow. |
Early MFD scanners
Early all-in-one machines were excellent for convenience and poor for difficult originals. Their automatic exposure tries to make the whole page pleasant, not faithful. A faint pencil note may be erased while a coffee stain becomes a landscape.
If the document matters, scan once in grayscale without "text enhancement" and once as bilevel text. Keep both. The ugly grayscale image often explains the mistakes in the clean text version.