The IPTC schema was originally designed by the International Press Telecommunications Council for newspapers to use when transmitting images electronically. IPTC is now the standard schema used by image editing and cataloging software to describe the content and ownership of the pictures.
While the IPTC schema continues to be among the most widely supported metadata standards, it has become so large that it’s not fully supported by very many applications. In practice, this means that some fields are ignored if the software maker does not feel it is useful to their customers. Nevertheless, the IPTC schema remains the bedrock of image metadata in use today. Let’s look at the evolution of the IPTC standard.
The original IPTC schema, referred to as the Information Interchange Model (IIM), was created in 1991. It defined some useful fields for tagging images and provided a way to write that information into the header of the file. If you open the Metadata panel in Adobe Bridge, you can see the IIM fields broken out, as shown elow. File formats that can support this type of metadata include TIFF, PSD, JPEG, DNG, and many proprietary raw formats.
Here are some of the IPTC IIM fields as shown in Adobe Bridge. You’ll see that there is duplication between these fields and some of the ones below. I have only included a portion of the IIM fields to save space.
IPTC Core / IPTC4XMP
Unfortunately, the specification for IIM was limited. The file header space where the data is written is size-limited. Additionally, it was soon apparent that more fields were needed to properly describe images.
In 2004, the specification was revised in two important ways. First, additional fields were added to more fully describe an image, including the ownership and credit information. Plus, the method for embedding the data in the file was changed to make use of Adobe’s XMP technology. The XMP space in a file is elastic, allowing data of almost any size to be written there.
In the following screenshots, we show the IPTC fields as they appear in Photoshop CC. Each field has a notation of the intended use of the field. Note that some fields, such as Photographer, appear in more than one panel. In these cases, the panels both point to the same underlying field, the IPTC Photographer field.
The IPTC organization continues to add new fields to the IPTC schema. These fields address omissions and ambiguities in the original fields.
As you can see, the extensions of the IPTC schema include a lot of connectivity to other databases through the use of unique identifiers. There is a lot of flexibility here, but that also comes with some significant difficulty of implementation. Support for these fields is pretty sporadic.
The IPTC standard continues to evolve, with small yearly changes. These changes frequently include the addition of namespaces from other schemas to the photo metadata standard, such as the 2017 addition of Star Ratings from the Adobe schema.