IPTC is the most commonly used schema for describing images and image ownership. The IPTC data can be split up into several categories that represent different classes of information. The IPTC specification has been revised several times since it first appeared in the 1970's.
The IPTC schema is a set of tags that were 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. keywords and ratings are not IPTC; they are examples of custom metadata.
The original IPTC schema, referred to as the Information Interchange Model, or 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 se the IIM fields broken out, as shown in Figure 1. File formats that can support this type of metadata include TIFF, PSD, JPEG, DNG, and many proprietary raw formats.
|Figure 1 shows the Metadata panel of Bridge with IPTC IM, showing these fields are written to the file header. This screenshot shows the fields and includes a short description of what tags can be placed in the fields.|
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 2005 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 CS4. 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.
Because the IIM fields live in both the file header and the XMP space, it's possible to have different tags in each one. Some programs, for instance, don't support the IPTC4XMP and only write tags into the IIM area. Some programs will attempt to resolve this in the background, making sure that the tags in each version of the Headline field, for instance, are matching. If you have a lot of image files annotated with software that does not write IPTC4XMP, then you may want to do some work to see that you're not destroying the old tags when you update a new tag.
Unfortunately, there are not easy and universal ways to resolve this. The first step is to find out if there is a problem. If you see tags attached to your images in one program that don't show up in another, this is a pretty likely explanation.
The Creator fields show the name and contact info for the photographer.
|Figure 2 IPTC creator fields|
The IPTC4XMP revision added a number of fields that describe usage rights. Here's the Photoshop panel. Note that the Copyright Status field is not part of the IPTC schema. It's a field that Adobe defined, as is the Copyright Info URL.
|Figure 3 IPTC rights and usage fields|
The IPTC Image and the IPTC Content panels in Photoshop's File Info offer a place to put lots of tags describing the image. Some of these fields, such as Intellectual Genre and IPTC Scene, are for use with a controlled vocabulary that is most appropriate for newspaper publishing. Some fields, such as Keywords, are useful for almost everyone.
|Figure 4 IPTC description fields|
While it's possible to write the location a photo was taken into a free-form field such as the Keywords field, we strongly recommend that you use each field for its intended purpose. The keyword Intercourse, for instance, has significantly different meaning than the city Intercourse, PA. Figure 5 shows a screenshot of the IPTC Location fields from Photoshop.
Not all image locations fit neatly into the Location/City/State/Country schema. An image may have a Location, such as Grand Canyon that does not belong to any City. In this case, you can enter Grand Canyon into the Location field and simply leave City blank. Images shot at sea may not be classifiable in any of the location terms. In this case, we recommend that you choose a method, such as noting the locations as "At Sea", and tag images as consistently as you can. Of course, in these ambiguous instances, GPS data is probably the best location identifier.
|Figure 5 IPTC location fields|
In 2008, the IPTC organization approved a new set of fields to add to the IPTC schema. These new fields attempt to address omissions and ambiguities in the original fields. Figure 6 below groups the new fields into four categories.
- Tags to describe the source image file.
- New tags to describe the image content.
- Resolving ambiguities in the Location fields – for example, the Location fields above do not specify if they refer to the location of the camera or the field of view.
- New tags that are designed specifically for cultural heritage institutions such as museums. These groups needed a standard way to describe artwork shown in a photo.
Support for new tags
Few programs support these fields currently (IDimager does). We expect it will be a while before they are commonly supported. The tags themselves are written in the form of XMP data to the files, so even older versions of Photoshop could support the new schema, once panels have been developed to show the tags.
|Figure 6shows the new file and content descriptions in IPTC Extended.|
The IPTC Extended schema also defined new tags to specify the license attached to any particular image, including model and property releases.
|Figure 7shows the new fields in the IPTC Extended schema that deal with rights, licensing, and ownership.|
For a complete look at the IPTC specification, check out their website.