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Quality control must be maintained throughout the life cycle
of an image collection. Routines must be developed to verify both
documentation (description, indexing, and metadata capture) and image
capture and maintenance. Time and labor limitations may mean that
it is only feasible to spot-check projects, in which case the frequency
of such checks must be decided: for instance, one image in every
ten, or every hundred, will be scrutinized.
Consistent image-capture guidelines and parameters should be established,
and scans must be periodically reviewed and checked for accuracy,
ideally against the source material, whether they are produced in-house
or supplied by a vendor. Although automatic scanning is generally
consistent, problems with exposure, alignment, and color balance
occur often enough to require a quality-control component in any
scanning program. Without quality control, it will not be possible
to guarantee the integrity and consistency of the resulting digital
image files. Steps should be taken to minimize the variations between
different operators and different scanning devices. The operator
and device, as well as the settings used, should be recorded for
each scan; this can normally be done in bulk, and standardized settings
can be developed for certain categories within the collection. Records
need to be proofread and mechanisms such as controlled vocabularies
utilized to ensure consistent data entry. Additionally, relationships
between cataloguing records and image files need to be verified and/or
developed.
Quality control must also be applied to all access files derived
from master images and to all preservation copies made, on whatever
media, as mistakes and technical errors can often be introduced during
the process of duplication or migration. Files should be checked
to ensure that all are correctly named, not corrupted, and so on.
Files should then be stored in a secure archival environment that
safeguards their authenticity and integrity, and quality checks should
be incorporated into a long-term management plan and performed on
a regular basis. There are various ways of ascertaining whether files
have somehow been altered or corrupted; one method is to document
and periodically compare checksums—the exact number of bits
in a file at its most basic, or actual values and patterns of data
using more complex checksum algorithms. Again, such measures require
that adequate preservation and technical metadata be stored along
with the image files. When selecting a networked storage solution,
evaluate software management capabilities for error checking and
file refreshing. CD-ROM error-checking software is also available.
(See Networks, System Architecture, and Storage and Security Policies
and Procedures.)
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