What your geotagged digital photos reveal about you

17 September, 2010 by Robert Vamosi
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The moment is special: your kid just learned how to ride a bike without training wheels. So you fire up your iPhone’s camera, snap a photograph, upload the image to TwitPic, and share the evidence of your child’s triumph via Twitter.

When you post the picture, a subset of the 75 million Twitter users can figure out the exact location of you and your child. Digital photos automatically store a wealth of information – known as EXIF data – produced by the camera. Most of the data is harmless, but as Mayhemic Labs’ Ben Jackson noted at the Next HOPE security conference in New York last July, about 3 percent of all photos posted on Twitter contain location data, and that figure is growing. Anyone on the web who can read the data can know where the photographer was standing.

Understanding EXIF data and geotagging

Created by the Japan Electronic Industries Development Association (JEIDA), the Exchangeable Image File format (EXIF) specification adds metadata to common JPG and TIFF image files. Along with a thumbnail image of the photo, EXIF data stores details about aperture, shutter speed, focal length, metering mode, and ISO settings. There’s also room for other information, such as the camera’s make, model, and registration number, and in some cases location data, also called geotagging data.

Geotagging is the process of storing latitude and longitude data inside an image’s EXIF data. This information pairs the image with a photographer’s specific geographic location, which mapping services such as Google Earth can then chart.

For older digital cameras, adding location data to an image requires editing the images on your computer, or using external hardware. But many newer digital cameras and camera phones have built-in GPS receivers. The geotagging features in these newer devices are integrated and seamless, and your EXIF files may store latitude, longitude, time (in the form of Coordinated Universal Time or UTC readings), and even altitude data (which can be helpful for reconstructing a family vacation on a map). With the explosion of smartphones today there is an increasing number of geotagged images posted to the web.

Remove geotagging data from your images

Some people don’t mind sharing their real-time location data with strangers, as is evidenced by the popularity of FourSquare and Facebook‘s new Places feature (although the latter is not yet available in Australia). But others may dislike the idea that strangers can know where they are at any given time. Fortunately, there are ways to keep geotagging data out of your final online images.

Many smartphones let you turn off the photo geotagging feature. On an iPhone, you can block geotagging by disabling all geolocation apps. To do so, go to Settings -> General, and toggle the Location Services settings to Off. In iOS 4, you can disable location services for specific apps (for instance, off for the Camera app but on for Yelp). If you don’t use iOS 4, instead of turning off Location Services for the entire phone, you can reset the Location Warnings. Go to Settings, tap Reset, and select Reset Location Warnings. Start the camera, and answer No to the ‘Ask on first use…’ question. You can then allow or disallow individual apps the next time you open them.

On Android phones, turning off GPS will break all location-based apps on the phone. Instead, start the Camera application, and under Location and Security in the menu on the left side, disable GPS. If you’re using the RIM Blackberry, press the Menu key, select Disable GPS, and select Yes to confirm the change.

If you’re using a point-and-shoot or DSLR camera, you can check the manual’s instructions on how to disable any geotagging features in-camera. But if you’d like to keep that data for your personal use but strip it out of publicly shared files, you have a few other options.

You can tweak the sharing settings on your online galleries – for example, Flickr has a Geo Privacy settings page that allows you to choose who can see location information. In iPhoto, you can export your photos for the web by going to File -> Export. In the resulting pop-up window under the Export tab, make sure the Include: Location Information box is unchecked.

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