Metadata is an essential partner for making the most of your images. It can help you sort and find them, control authorized uses, pinpoint them on a map, and make them look their best. This page provides an overview of different kinds of metadata plus how to help you with metadata handling issues.
"Image files without metadata are just a pile of pixels." – Bruce Fraser
EXIF – camera-created information
IPTC – user classification
How does metadata get there?
Ownership and licensing metadata
Image content information
Parametric Image Edits
Metadata handling: embedded, sidecar, catalog
Why can't I lock metadata?
Metadata is information about your photographs. This ranges from the mundane (the date the picture was made, what camera was used) to the sublime (what kinds of concepts the photo helps illustrate). You can use metadata to describe just about any characteristic of a photo: where it was shot, how much you like it, specific subject matter, usage rights and more. Metadata is also used by Parametric Image Editing software, (PIEware) such as Lightroom, to record image adjustments.
Different bits of metadata are called tags, and a particular tag will refer to some specific property of an image file. You can attach tags, such as keywords, to your images to later identify what a picture is about. Because catalog software can show you all images with a particular tag, you can easily collect all images about a particular subject while hiding any other images that don’t have that tag or combination of tags. The ability to filter a collection by tags is the key to making sense of a large library of photos.
A tag lives in a field, such as the International Press Telecommunications Council (IPTC) City field, which provides information about the tag itself. Is San Francisco the location of the photo or the address of the photographer? If it’s in the IPTC City field, it means the location of the photo. If it’s in the IPTC Author City field it refers to the address of the photographer.
A namespace describes the field and defines which kinds of tags are acceptable to put there — for example, “Write the name of the city where the photograph was created.” A namespace may limit the kind of entry that can be entered in a field. The namespace for a date field, for instance, may only allow information to be entered in some kind of date notation. A collection of namespaces is called a schema.
There are a few widely supported schemas, but anybody can publish a schema. The EXIF (Exchangeable Image File Format, pronounced ex-if) schema is a set of rules that camera makers follow to tag images with information – for instance, the time of the photo and the camera settings. The IPTC schema is a set of tags that were originally designed 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. Your PIEware uses yet another schema to describe the adjustments you make to the images, such as the Adobe Camera Raw schema or the Capture 1 schema.
Exchangeable Information File Format (EXIF) is a standard used by camera manufacturers to store camera-created information in the file. This includes camera settings like aperture and shutter speed as well as information like the white balance selected for the image. EXIF also describes the characteristics of the image data itself so programs can know how to open the file properly. In general, EXIF is not supposed to be edited after capture, with the exception of correcting a camera's date/time setting and adding GPS data.
Read more about EXIF
The International Press Telecommunications Council, or IPTC, metadata is probably the most familiar metadata to photographers. It includes fields to tag the photographer's name, rights and location of the photo, keywords, captions and more. If you open the Photoshop File Info panel, much of the metadata in there is IPTC metadata. The IPTC schema has gone through several revisions, including one that was finalized in summer 2008. We suggest you familiarize yourself with IPTC metadata fields to make use of the ones that will add the most value to your work.
Read more about IPTC
XMP is not actually a schema but rather a method to write metadata. It's a particular flavor of XML that Adobe developed for the storage of metadata. Many photographers think XMP is a kind of file, since Adobe Camera Raw creates an XMP sidecar file when adjusting raw images. In fact, those .XMP files are really text files with XMP-formatted text.
Read more about XMP
There are three basic ways that metadata gets created.
Some kinds of metadata, such as the EXIF information your camera creates, are produced automatically, with no real work by the photographer (other than, say, setting the clock in your camera correctly). Mostly, automatic metadata describes camera data or characteristics of the file such as size and type.
Some information can be applied to lots of photos at the same time. This can include the name and contact information for the photographer, and it also might include a description of the subject matter, such as the location where the pictures were made, or the name of the assignment. Bulk metadata is most often created with the use of a metadata template.
Some metadata can only be created for a few images at a time; this is called custom metadata. One example of customer metadata is the rating you apply to indicate how much you like the image. Custom keywords can be assigned to images where the subject matter changes from shot to shot. And the parametric image editing instructions are also often custom metadata since you adjust images individually to get the best look.
The easiest way to add bulk metadata to your images is with a metadata template. Many programs offer the ability to save groups of tags, such as the photographer's name and contact information. We suggest that you apply metadata templates that contain contact and licensing information, as well as some subject matter descriptions, as early in the workflow as possible. Check out the metadata templates page to see how to create and apply these to several popular programs.
Read more about metadata templates
The most basic sets of tags you'll want to apply to your pictures are those that identify the photographer. Figure 1 shows the File Info panel from Photoshop CS4 with the IPTC Contact panels displayed. You can list your name, address, phone, email and web contact information here. This is particularly important information to fill out since it prevents the images from becoming "orphans."
|Figure 1 shows Photoshop's File Info panel. Fill in your contact information so that people will know the source of the image.|
The IPTC schema has a number of fields that can specify the usage rights attached to an image. In Photoshop, you can find these in the Description panel and the IPTC Status panel. There are also two fields that are Adobe-created fields that help define ownership and licensing. Figure 2 shows these two panels.
Note that the "Copyright Status" tag is not currently part of Adobe's metadata templates. We've created a special script you can download for free. You will be able to apply the Copyrighted tag to many images at once.
Read more about this script in Metadata Templates
|Figure 2 shows the Photoshop's Description and IPTC Status panels.|
The Picture Licensing Universal System is a metadata schema that can describe image licenses and much more. It's a comprehensive system of industry standards for image licensing allowing photographers, illustrators, artist reps, stock agencies, and other image licensors to clearly communicate license information to their customers in a machine-readable format. Its purpose is to automate the process of managing and tracking image licenses. Figure 3 shows the web-based PLUS license generator that you can use to create a PLUS-compliant license code.
For more information, check out useplus.org.
|Figure 3 shows the PLUS web interface. You can generate custom license codes with the PLUS tools.|
The Internet has opened publishing to the entire world, including many who have little knowledge of licensing issues. Creative Commons (CC) is an effort to democratize licensing so it is within reach of everyone who is connected to the Internet. All Creative Commons licenses allow the sharing of material in at least a non-commercial way. (Any CC-tagged item can be used for a school report, or a private email, or printed and put up on a wall at a person's home.) All Creative Commons licenses require that any used image be accompanied by a credit.
CC has developed a simple set of licensing categories and translated it into many languages. It has also developed a set of icons to describe different kinds of licenses that can be attached to the images as shown in Figure 4. With a CC license, you may limit the following:
- Attribution: specifies whether publication of the work must be accompanied by credit for the author.
- Commercial Uses: specifies whether the work may be incorporated in traditional commercial uses, such as advertisements.
- Derivative Works: specifies whether the work may be changed or must always be displayed in original form.
|Figure 4shows the different Creative Commons licenses available.|
There are many fields, particularly in the IPTC schema, that can help you describe images. They won't all be needed for all images (in fact, many people can get by with just a handful of descriptive terms for most of their images).
Read more about the full IPTC Schema
Keywords are words or phrases that you associate with a picture to describe the subject matter, style, uses or connotations of the image. These descriptions can be of great use when organizing and searching your picture collection. For many people, the most important keywords are those that describe the shoot in very general terms – the client, project or situation name. This can also include the name of people pictured. There's no single right way to keyword an image. Proper keywording will be dependent on who is searching the collection and what's in it. Let's look at a few considerations.
Keywording for internal or external usage
Your keyword strategy should first address who is searching the collection and why. If the objective is to provide the photographer a way to find images in his own collection, the shoot names and a few broad subject categories may be all that's needed. If the objective is to have an image found in a stock search, then the keyword needs are much more extensive. You may want to add keywords for lots of subject classifications, as well as concepts the photograph might help to illustrate.
One way to ensure that keywords (or any other metadata tags) are created consistently is to use a controlled vocabulary. In general, this refers to a structured list of approved terms that can be used as tags. Some programs support a highly restricted controlled vocabulary, and some are almost completely free-form.
Read more about Controlled Vocabulary and Keywords
The IPTC schema provides a way to write the location of the photograph into metadata. The fields are arranged in a natural hierarchy from the country's name, down to the more specific location labels. While this does not work for all images (images on the high seas, for instance, or images shot on a river that defines a border), it works for the vast majority. By putting the location name in an IPTC defined field, you make the data much more valuable. The keyword "New York" is much less valuable than a tag in the IPTC City field that defines the location of the photo as the city of New York. If there is no city, it's okay to skip that and use Country/State/Location, such as USA/Arizona/Grand Canyon.
IPTC location fields are increasingly being tied to GPS data since databases can now identify location names from the GPS coordinates.
|Figure 5Photoshop's IPTC Location fields.
The caption is a long-form description of the content of the image, usually in grammatically correct form. Captions are a widely supported field, so people tend to input a wide variety of non-caption-related information into this field over time. We suggest that you use the field in its intended way, and use other fields, such as the contact fields, to hold non-caption information.
There are a lot of other fields to describe particular aspects of a photograph. For a more complete listing of available fields, check out the IPTC page.
Read more on IPTC
Ratings are one of the most valuable forms of higher metadata — in many ways they are the key to a streamlined digital workflow. By using ratings comprehensively, you make your best images easily discoverable, even if your collection is very large. A systematic use of ratings also lets you focus more of your time on your best pictures since they will be so easily identified.
|Figure 6 A representation of a collection with ratings applied. As you can see, a collection becomes a lot easier to search if it is divided into sections. By making broad classifications of subject matter (the vertical lines) and adding ratings (the horizontal divisions), you can find your desired set of images more easily. You can, for instance, search only through your best images (at the top of the pyramid) for a particular photo. If you find something that’s close to but not exactly what you want, you can follow that thread downward to see if there is a more appropriate image included in that subject matter group.|
One of the most promising new technologies for organizing and sorting images is the use of GPS data. GPS data is becoming a rich tool for photographers since more cameras and software are taking advantage of what it has to offer. There is an increasing number of ways to tag your images with the GPS coordinates of the shoot.
|Figure 7 An image in Expressions Media 2 and that image's location in Google Maps. GPS can be a very helpful way to organize an image collection.|
When you alter an image with a parametric image editor like Lightroom, Capture One, or Bibble, the instructions for adjusting your image are also saved as metadata. For proprietary raw files, the instructions will be saved in a sidecar file unless the software is made by the camera manufacturer, such as Nikon Capture NX or Canon DPP.
Read more about Parametric Image Editing
Metadata generally lives in one of three places: embedded in the file, in a sidecar file, or in an image catalog.
- Metadata that is embedded in the file is the most portable, and therefore probably the most durable. Of course, in order to embed the metadata you need to use a file format that supports embedding. Proprietary raw files often don't allow flexible metadata embedding.
- When a file format does not support embedding, the metadata is often saved in a sidecar file – usually a text file that lives in the same folder as the original file and is named in a similar fashion. Sidecar files can also refer to an entire folder full of images and live in the folder as a single file. Capture One uses this system to store image editing instructions.
- Catalog software can "harvest" the metadata in a group of files and save it in the catalog document. Most catalog software allows the user to push the data back into the file or sidecar files if you'd like to keep the files up to date.
If metadata is so valuable, shouldn’t you be able to lock it to the file? Shouldn’t Adobe or somebody just make it so that metadata is permanent and can’t be stripped away? We hate to be the bearer of bad news, but it’s just not possible. Existing software and file formats don’t support locking, and there’s no magical way to make them do that.
Theoretically, you could lock metadata by making a new file format that is unsupportable by current software, yet that makes it impossible to convert to a TIFF or JPEG. This hypothetical new format would be a pretty tough sell. It's unlikely many people would be willing to use a file format that could never be converted to the universally accessible formats already in use.