Securing Digital Image Assets in Museums and Libraries: A Risk Management Approach

Library Trends, Fall, 1999 by Teresa Grose Beamsley

It is now possible to identify potential risks that are associated with each type of concern. Changes in the integrity of digital image information can be caused by direct modifications made to the image data. They may also be associated with modifications to contextual data that limit understanding and interpretation of the associated surrogate image. The destruction of the mechanisms that link contextual data to the appropriate digital image has the same effect as deleting contextual information. Loss of control over digital assets can be the result of failure to establish ownership and/or copyright. Even if copyright is established and enforceable, failure to enforce rights has the same effect as having no rights at all. Failure to detect corruption of digital information means that invalid, partial, or inappropriate information will be spread under the guise of authentic reliable information. Each of these risks represents the possibility of an information systems failure.

PRIORITIZING RISKS--How SAFE IS STANDARD PRACTICE?

What are the chances that any of these risks will be realized? An examination of the typical ways in which digital image information and associated contextual data are created, managed, and made accessible sheds light on the probability of content degradation. Most institutions already employ both active and passive measures to prevent or minimize the impact of a reduction in reliable content in systems that depend on the use of digital image information. Do these efforts have any effect on the immediacy of each risk?

CREATING DIGITAL IMAGE FILES AND DERIVATIVES

A digital image cannot be a better representation than the best available from the conversion method used to create the image. A number of authors and research groups have conducted comparative studies of conversion techniques and produced recommendations for best-practice conversion methods, ranging from direct digital photography through microfilm and negative scanning to direct positive scanning and PhotoCD processing (http://www.columbia.edu/acis/dl/imagespec.html) (Kenney, 1997; Conway, 1996; Reilly, 1995). Similarly, the digitized image cannot be better than the source document or object without some sort of data modification. It is not necessary to belabor the importance of informed decision making in the process of creating archival image files from which derivative files may be drawn. Frey (1997) suggests that four targets be used for objectively evaluating the results of digitization: tone reproduction, color reproduction, detail and edge reproduction, and noise. Satisfactory performance in output tests of all four targets will guarantee that, at least at the archival level, an acceptably accurate digital representation of image information has been created.

The integrity of digital image information is inherent in the structure of the image file. Only bit-mapped images (those created from aggregations of discrete bits or units of data) are considered in this discussion; vector image data are created and used in museum and archival environments much less frequently than in academic libraries and special collections. The parameters that are chosen to define file structure determine the limitations of the file as an image surrogate. These parameters include dynamic range, resolution, and compression (Besser et al., 1995).