Embedded metadata for photographs
Wanneer je archief veel digitale foto’s bevat, kan je overwegen om extra metadata in de bestanden in te bedden. Op die manier garandeer je dat de foto’s en de bijhorende identificerende gegevens niet van elkaar gescheiden kunnen worden.
In deze tool leer je het volgende:
- Wat zijn ingebedde metadata?
- Wat zijn de voor- en nadelen van ingebedde metadata?
- Hoe voeg je extra ingebedde metadata toe aan foto’s?
Metadata are structured data that contains information about the identification, management, type, usage and storage place for physical or digital sources. It is data about data. We distinguish two types of metadata:
- Descriptive metadata: details about the content which helps you to identify, contextualise and find your images;
- Administrative metadata: information about managing the source such as rights management, the relationship between individual sources that together form a whole, preservation and conservation, and your images' technical properties (resolution, bit depth, etc.).
The metadata for digital sources can be stored both inside and outside the described file. If the metadata are stored outside the described file, they are usually found in a separate spreadsheet or database.
If metadata are stored within the file itself, they come in the form of embedded metadata. The metadata can no longer be separated from the content they describe because they are linked to the relevant digital file, thus the digital file becomes self-descriptive.
Embedded metadata are widely used for digital photo files. This primarily involves technical (administrative) metadata such as a time stamp and information about the camera, settings and GPS coordinates. These metadata are generated automatically when a picture is being taken. You can supplement these metadata yourself with additional details that describe the image's content and context, e.g. the title and year of the photographed artwork, title of the piece, name of the photographer, applicable licence, etc.
Why embed metadata?
Adding additional embedded metadata to digital images is important for managing and providing access to the photos in question. By embedding content-related metadata into the image, you'll ensure that the digital file and associated identifying and descriptive information cannot be easily separated from each other.
For printed photos and audiovisual media, the descriptive information about a piece of work is often physically attached to the carrier, e.g. writing on the back of the photo that states who or what is on the photo, labels or packaging for a vinyl record or video cassette with details about the contents. This physical connection means the descriptive information is always kept together with the actual object.
The embedding of metadata follows the same principle and can be likened to information being written on the 'back' of the digital image, so it cannot be separated from the image and the link between file and descriptive information is always retained. Embedding additional metadata also improves the searchability of your photo collection, especially once you've added details about the content.
- Embedded metadata improve the findability of digital files, e.g. so you can use search engines to look for specific metadata.
- When you distribute digital files for (re-)use, the embedded metadata are often sent together with the digital files. This allows the (re-)user to identify who or what is depicted on the photo, who took the photo, and under what conditions the photo can be (re-)used.
- The embedded technical metadata are always updated when the digital file description changes, so it always remains current.
- Metadata added by the digital file users can be automatically written to your own database.
- When derivatives of an original file are created, the embedded metadata may not be copied across, in which case it needs to be added manually afterwards.
- When migrating digital files to a different format, it's possible that certain metadata is overwritten or replaced.
- Metadata that are managed in a centralised database can be easily added or edited in bulk, but embedded metadata needs to be edited per file or you need to use external software.
- If it is no longer possible to open files with embedded metadata, the metadata may also stop being accessible.
When do you add metadata?
In order to prevent important information becoming lost, it is best to add metadata to a digital photo file as soon as possible. Archiving digital images presents a good opportunity to check what metadata are already embedded with the image and what information you still need to describe the image further (see also the Create an access pass and describe your archive article). Images that originate from a digital source mostly already contain embedded (technical) metadata, which can be expanded with details about the content. Technical metadata for digital photos are usually created automatically and only need to be verified, but you need to add metadata about the content yourself.
Images that come from an analogue source and have been digitised also need to be given the correct metadata (see also the article on High-quality text and image content digitisation). In contrast to images with a purely digital origin, you'll need to create and add technical metadata for digitised analogue photos yourself.
A potential problem here is that technical metadata for analogue photos have often not been updated, so they cannot be added to the digitised file. Check to see what data you can still find and add them. Some metadata, such as the resolution information, are created when an analogue photo is digitised.
Not all information necessarily needs to be embedded as metadata within the images. A clear folder structure for your digital archive often provides lots of contextual information. (See also the Draw up an organisational plan/folder structure and Naming files and folders) articles for this. For example, you don't need to embed content metadata for each individual photo in 'New_Year_Party_2019' to indicate that it's from that specific party.
It is best to add content metadata as soon as possible while the information is still fresh in the memory. The longer you wait, the more information might be lost.
How can you add and edit metadata?
Most software programs that are used for opening or editing photos allow you to see the file's embedded metadata.
Online tools such as Metapicz and Exifdata show you the embedded metadata that are stored within a photo. Photo editing software such as GIMP (free and open source) and Adobe Photoshop (paid, proprietary) allows you to look up (an often limited set of) metadata for a digital photo file and edit the metadata fields.
Which standards do you use?
Digital file management can involve all kinds of software, all of which requires the embedded metadata to function optimally. It is therefore important that all these different software programs can read the embedded metadata without any problems. Using international standards makes this possible. These standards ensure the software knows where and in what form it can find the embedded data in a digital file. Some common standards include: IPCT Photo Metadata Standard, Exif and XMP.
IPTC Photo Metadata Standard is a standard for describing photos that is used worldwide by news agencies, photographers, libraries and museums, among others. IPTC structures and defines metadata properties so that users can add precise and reliable details about the people, places and objects depicted. This includes dates, names, information about rights, and identifiers relating to the creation of the photo. The standard can be used for common formats such as JPEG, TIFF and PNG. See also the article on Recommended file formats for keeping your digital archive readable.
Exif (Exchangeable Image File Format) is a standard for embedded metadata that is often used for photos (mainly JPEG and TIFF files), but which also works with audio (WAV) files. The Exif standard cannot be used for GIF, JPEG2000 and PNG files, however. It includes details about when the photo was taken, camera settings, GPS information, copyright information, descriptions and a preview thumbnail.
XMP information (Extensible Markup Platform) is mostly also included together with the IPTC and Exif data. This standard allows existing metadata formats that do not fit into it to be retained alongside the XMP format. XMP can be used for AIFF, GIF, JPEG, JPEG2000, MP3, MP4, PDF, PNG, PSD, TIFF and WAV files.