EXIF: The Hidden Data Inside Your Digital Photos

If a picture is worth 1,000 words, a digital photo is worth 1,001. When you hit the shutter button on your digicam, the device in your hand records the light its lens sees — but that’s not all. Each digital photo you take has a variety of data fields embedded inside of it, visible only to those who know exactly where to look.

What is EXIF Data?

We’re talking about metadata here, which is to say, data about data. Metadata are adjectives; the purpose of each piece of metadata is to describe something else. The specific kind of metadata recorded inside your digital photos is EXIF data, which stands for Exchangeable Image File Format. EXIF data is recorded in a separate portion of your image file than the visual, photographic data, and therefore cannot be seen or detected by looking at the image. Instead, examining EXIF data requires special software to extract and display those fields.

What Gets Recorded?

Fig. 1 - A photo containing EXIF data. Click it to see the data.

All sorts of data relating to the photograph is stored in EXIF fields. When you snap a digital photo, the camera records a variety of things, such as:

• The camera model.
• Exposure time.
• The lens’ focal length.
• Aperture size.
• Sensor sensitivity.
• Whether or not the flash fired.
• Date & time the picture was taken.
• The type of lens used.

If your camera has a GPS unit, it might even record your geographical location at the time you took the photo. Many cameras can also be configured to record your name as the photo’s author.

Many individual camera manufacturers such as Nikon and Canon also record their own custom EXIF data fields on your photos. There are many more EXIF data fields recorded depending on which camera you use. The ones mentioned here are just the basics.

The palm tree photo you see if figure 1 contains EXIF data. Click on it to view those EXIF data fields, courtesy of Flickr.

Your computer also records EXIF data

Your camera might not be the only source for EXIF data. Depending on what software you use to import your digital photos to your computer, that software might make additions to your photo’s EXIF data fields. For example, importing a photo with Apple iPhoto records the version of Mac OS X you’re using, and “Quicktime” as the software used during import.

How to View EXIF Data

Viewing EXIF data requires special software that knows exactly where to look. Here are a few options:

• Windows PC: ExifPro Image Viewer acts like Explorer, but displays all of the EXIF data contained in each photo it finds.
• Mac OS X: Click on a photo, hold CMD, and press I. Inside the new window that appears, expand the “More Info” section.
• On the Web: Flickr, a fantastic photo sharing site, is able to find all the hidden EXIF fields inside your photographs. Upload a photograph to your Flickr account, go to the photo’s page, and click the “more properties” link that’s located in the right-hand sidebar.

EXIF data provides an interesting insight into the art of digital photography. If you have a camera that gives you manual control over it’s settings and you’re getting curious about how to use them, EXIF can be a fantastic learning tool. Examine the EXIF data of photos taken in automatic mode, and try to understand how each one affects the photo that’s been captured. Browse around Flickr, and look at the settings recorded in the photos of your favorite photographers.