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Web privacy: How online photos reveal more than you know

Geotagging data lets strangers know exactly where you are

The geotagging data contained in many mobile phone images can let strangers know exactly where you are and what you've been up to. We find out just why you should be careful when posting digital snaps online.

Digital cameras and cameraphones mean you can snap those special moments to your hearts content, preview the shot and erase and re-take if necessary.

The technology gets even better thanks to the help of social networks such as Twitter and Facebook, which let you share those special moments with your friends, family and followers around the world.

However, its worth stopping and thinking about the fact that when you post the picture on a social network, millions of web users across the globe can discover the exact location you were in when you captured the shot.

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 recently, about three percent of all photos posted on Twitter contain location data, and that figure is growing. Anyone on the web who can read the data knows where the photographer was standing. And arguably this is a gross invasion of personal privacy.

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, some of which can help a printer do a better job of colour-matching the final printed image. There's also room for other information, such as the camera's make, model, and registration number, and in some cases, location data.

Geotagging is the process of storing latitude and longitude data inside an image's EXIF data. This information mates 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 complicated peripherals: You must attach a cable to the camera to communicate with a GPS receiver, such as a stand-alone navigation device or a mobile phone. But many newer digital cameras and mobile phone cameras 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, Jackson is seeing an increasing number of geotagged images posted to the web.

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