The IPTC is happy to announce the latest version of our guidance for mapping between photo metadata standards.

Following our publication of IPTC’s rules for mapping photo metadata between IPTC, Exif and schema.org standards in 2022, the IPTC Photo Metadata Working Group has been monitoring updates in the photo metadata world.

In particular, the IPTC gave support and advice to CIPA while it was working on Exif 3.0 and we have updated our mapping rules to work with the latest changes to Exif expressed in Exif 3.0.

As well as guidelines for individual properties between IPTC Photo Metadata Standard (in both the older IIM form and the newer XMP embedding format), Exif and schema.org, we have included some notes on particular considerations for mapping contributor, copyright notice, dates and IDs.

The IPTC encourages all developers who previously consulted the out-of-date Metadata Working Group guidelines (which haven’t been updated since 2008 and are no longer published) to use this guide instead.

CIPA, the Camera and Imaging Products Association based in Japan, has released version 3.0 of the Exif standard for camera data.

The new specification, “CIPA DC-008-Translation-2023 Exchangeable image file format for digital still cameras: Exif Version 3.0” can be downloaded from https://www.cipa.jp/std/documents/download_e.html?DC-008-Translation-2023-E.

Version 1.0 of Exif was released in 1995. The previous revision, 2.32, was released in 2019. The new version introduces some major changes so the creators felt it was necessary to increment the major version number.

Fully internationalised text tags

In previous versions, text-based fields such as Copyright and Artist were required to be in ASCII format, meaning that it was impossible to express many non-English words in Exif tags. (In practice, many software packages simply ignored this advice and used other character sets anyway, violating the specification.)

In Exif 3.0, a new datatype “UTF-8” is introduced, meaning that the same field can now support internationalised character sets, from Chinese to Arabic and Persian.

Unique IDs

The definition of the ImageUniqueID tag has been updated to more clearly specify what type of ID can be used, when it should be updated (never!), and to suggest an algorithm:

This tag indicates an identifier assigned uniquely to each image. It shall be recorded as an ASCII string in hexadecimal notation equivalent to 128-bit fixed length UUID compliant with ISO/IEC 9834-8. The UUID shall be UUID Version 1 or Version 4, and UUID Version 4 is recommended. This ID shall be assigned at the time of shooting image, and the recorded ID shall not be updated or erased by any subsequent editing.

Guidance on when and how tag values can be modified or removed

Exif 3.0 adds a new appendix, Annex H, “Guidelines for Handling Tag Information in Post-processing by Application Software”, which groups metadata into categories such as “structure-related metadata” and “shooting condition-related metadata”. It also classifies metadata in groups based on when they should be modified or deleted, if ever.

Collaboration between CIPA and IPTC

CIPA and IPTC representatives meet regularly to discuss issues that are relevant to both organisations. During these meetings IPTC has contributed suggestions to the Exif project, particularly around internationalised fields and unique IDs.

We are very happy for our friends at CIPA for reaching this milestone, and hope to continue collaborating in the future.

Developers of photo management software understand that values of Exif tags and IPTC Photo Metadata properties with a similar purpose should be synchronised, but sometimes it wasn’t clear exactly which properties should be aligned. IPTC and CIPA collaborated to create a Mapping Guideline to help software developers implement it properly. Most professional photo software now supports these mappings.

Complete list of changes in Exif 3.0

The full set of changes in Exif 3.0 are as follows (taken from the history section of the PDF document):

• Added Tag Type of UTF-8 as Exif specific tag type.
  • Enabled to select UTF-8 character string in existing ASCII-type tags
• Enabled APP11 Marker Segment to store a Box-structured data compliant with the JPEG System standard
• Added definition of Box-structured Annotation Data
• Added and changed the following tags:
  • Added Title Tag
  • Added Photographer Information related Tags (Photographer and ImageEditor)
  • Added Software Information related Tags (CameraFirmware, RAWDevelopingSoftware, ImageEditingSoftware, and MetadataEditingSoftware)
  • Changed Software, Artist, and ImageUniqueID
  • Corrected incorrect definition of GPSAltitudeRef
  • GPSMeasureMode tag became to support positioning information obtained from GNSS in addition to GPS
• Changed the description support levels of the following tags:
  • XResolution
  • YResolution
  • ResolutionUnit
  • FlashpixVersion
• Discarded Annex E.3 to specify Application Software Guidelines
• Added Annex H. (at the time of publication) to specify Guidelines for Handling Tag Information in Post-processing by Application Software
• Added Annex I.and J. (both at the time of publication) for supplemental information of Annotation Data
• Added Annex K. (at the time of publication) to specify Original Preservation Image
• Corrected errors, typos and omissions accumulated up to this edition
• Restructured and revised the entire document structure and style

Anyone who has managed photo metadata can attest that it is often difficult to know which metadata properties to use for different purposes. It is especially tricky to know how to tag consistently across different metadata standards. For example, how should a copyright notice be expressed in Exif, IPTC Photo Metadata and schema.org metadata?

For software vendors wanting to build accurate mapping into their tools to make life easier for their customers, it’s no easier. For a while, a document created by a consortium of vendors known as the Metadata Working Group solved some of the problems, but the MWG Guidelines are no longer available online.

To solve this problem, the IPTC collaborated with Exif experts at CIPA, the camera products industry group that maintains the Exif standard. We also spoke with the team behind schema.org. Based on these conversations, we created a document that describes how to map properties between these formats. The aim is to remove any ambiguity regarding which IPTC Photo Metadata properties are semantically equivalent to Exif tags and schema.org properties.

Generally, Exif tags and IPTC Photo Metadata properties represent different things: Exif mainly represents the technical data around capturing an image, while IPTC focuses on describing the image and its administrative and rights metadata, and schema.org covers expressing metadata in a web page. However, quite a few properties are shared by all standards, such as who is the Creator of the image, the free-text description of what the image shows, or the date when the image was taken. Therefore it is highly recommended to have the same value in the corresponding fields of the different standards.

The IPTC Photo Metadata Mapping Guidelines outlines the 17 IPTC Photo Metadata Standard properties with corresponding fields in Exif and/or Schema.org. Further short textual notes help to implement these mappings correctly.

The intended audience of the document is those managing the use of photo metadata in businesses and the makers of software that handles photo metadata.The IPTC Photo Metadata Mapping Guidelines document can be accessed on the iptc.org website. We encourage IPTC members to provide feedback through the usual channels, and non-members to respond with feedback and questions on the public IPTC Photo Metadata email discussion group.