Indexing and OCR for usable retrieval

Separate reliable fields from extracted text

An index can carry a record identifier, title, date, collection, roll or fiche reference, source frame, case number, account number, drawing number, or another customer-defined retrieval field. Each field should have a defined source and format. That structure lets an organization retrieve a known record even when a page contains faint text or a layout that is difficult for OCR.

OCR reads visible machine-printed characters from the available image. It can be delivered as a searchable PDF layer, plain text, or a structured text output when specified. It is useful for discovery, but it should not be described as proof that every word was read correctly or that every image is equally searchable.

Design fields at the right level

Collection-level fields establish context, such as record group, department, title, date span, or source system. Carrier-level fields can identify a reel, fiche, jacket, card, box, or drawer. Frame-level fields connect a digitized page or drawing to its source position. The useful levels depend on how users search and on what information actually exists in the material.

For jacket fiche, retaining jacket, channel, strip, and frame relationships may be important. For roll film, a reel and frame range may be appropriate. For aperture cards, a card identifier and drawing fields can preserve the relationship between card and mounted frame. A data dictionary makes these decisions visible before delivery.

Set OCR expectations from representative sources

OCR quality is affected by the entire image chain: the original document, filming, reduction, focus, density, contrast, scratches, cropping, and capture processing. Historical print, complex columns, unusual fonts, faint text, handwriting, and high-reduction images can produce uncertain text. Library of Congress guidance on historical materials likewise notes that OCR inaccuracies complicate searching.

A project can define languages, output form, sampling, treatment of uncertain text, and exception labels. It should not start from a universal accuracy percentage. When a field is operationally important, source-linked indexing or defined review is more dependable than assuming OCR will supply it everywhere.

Keep files, text, and metadata connected

A stable record identifier can join the image or PDF, OCR output, and metadata row or sidecar. The associated delivery manifest can record relative paths, file role, OCR status, source carrier reference, and exception notes. This design supports later import, reconciliation, and reprocessing without embedding every data decision inside a filename.

National Microfilm reviews field maps, OCR scope, exceptions, and delivery formats per project. We can prepare files and structured data for a customer-defined retrieval or document-management workflow, with requirements confirmed before production delivery.

Common questions