Long-term preservation of digital photographs

 

A black and white photo of a small boy holding a camera up in front of his face to take a photo - he is standing on concrete paving and wearing up a zip up parka.

Street portrait 8, Circular Quay, Sydney, NSW, Jon Lewis, 20 July 2014

What is photography? It is a term that covers historical material, family albums, snaps shared via social media platforms, artworks sold for millions of dollars and more. A digital snap on your phone is as much a photograph as a one-off print from a negative in a darkroom. The family album is now a computer, smartphone, hard drive or the cloud where thousands of images are stored but rarely looked at or printed out. Social media has changed the way we take photographs, as well as what we take photographs of — from food to countless other everyday occurrences. And with the shift to social media, photography is also becoming an experience that is sometimes ephemeral.

Memory and documentation sit at the heart of the medium of photography for collecting institutions, and the preservation of digital photography in the 21st century requires understanding and action by a growing number of stakeholders. This includes photographers, curators, archivists, librarians and historians who all play an important role in the life of a photograph. Digital photographs face immediate danger of loss and fragility when compared with their tangible, physical counterparts. Without proactive management and digital stewardship over time we could lose our ability to tell our stories and share our collective memories.

On Monday 23 September 2019, the National Library of Ireland (NLI) held the event ‘Digital Photography: Create, Curate and Save’ to explore the need for preservation of digital photography. I was honoured to be invited to Dublin by the NLI to speak at this event and highlight the importance of the long-term digital preservation of born-digital photographs. It provided the opportunity to get photographers thinking about digital preservation at the point of creation, and to understand how decisions on file formats and technical characteristics have long term impacts on accessibility and quality.

Photographers are required to devote a significant amount of time to the management of their digital files. Important aspects to consider at the point of creation include file formats and their technical characteristics, file names and metadata (both technical and descriptive).

File formats

The choice of file format depends on what is being used to create digital photographs, but it is best to aim for an uncompressed file format where possible. Cheaper digital cameras and smartphones (with default settings) will often only shoot in a compressed file format such as JPEG. High-end professional cameras and some apps on smartphones provide the ability to shoot in camera raw file formats, often proprietary. There are advantages and disadvantages for both.

JPEG is a compressed file format

  • each time a JPEG is saved, information is discarded
  • small file size with low bit depth
  • widely supported and does not require specialist software to view
  • suitable for access

Camera raw contains all the unprocessed data from the camera sensor

  • no matter how many times the file is processed, the raw data never changes
  • larger file size (compared to JPEG) with high bit depth
  • requires processing by specialist software for access
  • suitable for preservation

The State Library’s specifications and guidelines for born-digital photographs asks for the highest pixel dimensions as well as the highest bit depth available. What is bit depth? It quantifies how many unique colours are available in a digital photograph. Those with higher bit depths can use more shades or colours, improving image quality. When collecting digital photographs for long-term preservation, it is important to try and acquire the highest quality available. 

Where suitable, the State Library prefers born-digital photographs in the Digital Negative (DNG) camera raw file format. It is a publicly available archival file format created by Adobe and has been adopted as the native file format by some camera manufacturers. It is still under consideration as an international standard but is preferred by many collecting institutions and it an extension of the TIFF 6.0 format, and is compatible with the TIFF-EP standard (ISO 12234-2:2001).

File names

Cameras and phones will often create arbitrary, sequential file names that do not provide any useful information. Using descriptive file names that include the creation date and a brief description ensures that files can speak for themselves without having to open them or undertake any in-depth analysis.  

It is important to follow general file naming guidelines including:

  • only using alphanumeric characters (a-z, 0-9)
  • using hyphens or underscores instead of spaces
  • ensure file names end with a file extension
  • being consistent with file names

For example, 20191107_MyCat001.dng

Metadata

Technical and descriptive metadata are important for digital photographs and can provide much more valuable information when compared with traditional analogue photography. This is because cameras automatically record a lot of technical information that can be useful, such as the date/time of creation and the type of equipment used to take the photograph. It is important to make sure that the correct date/time is set in the camera to ensure this technical metadata is accurate and trustworthy. 

Descriptive information can be added to digital photographs, including who the creator is, copyright and information about the photograph itself. Various tools are available to view, extract and embed metadata.

Descriptive information is critical for the discoverability and provenance of photographs. When technical, descriptive, source, ownership and copyright metadata are embedded in an image, users and collecting institutions can properly identify and attribute them. It is important to consider sensitive information and whether you want that to be publicly accessible, for example your address and other contact details.

What does all this mean for collecting digital photography?

Archivists, curators and librarians need to develop an understanding of digital photography including file formats, technical specifications and metadata practices. They need to engage with photographers at the earliest point possible and determine the most appropriate file format for each acquisition. Accepting file formats such as camera raw need the appropriate staff knowledge and resourcing to manage.

Custodial emphasis should be placed on appropriate file formats and storage. Care needs to be taken with technical specifications that affect the integrity of the photograph, such as bit depth and colour profiles. Most importantly, acquisition of born-digital photographs must be approached on a case-by-case basis where specifications and standards do not apply to all scenarios. 

Read our blog post for examples on how the Library’s born-digital and digitised photographs are being used.

Written by Matthew Burgess, Digital Collections Analyst, for World Digital Preservation Day 2019.

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