When Adam Savage, host of the popular science program “MythBusters,” posted a picture on Twitter of his automobile parked in front of his house, he let his fans know much more than that he drove a Toyota Land Cruiser.
Embedded in the image was a geotag, a bit of data providing the longitude and latitude of where the photo was taken. Hence, he revealed exactly where he lived. And since the accompanying text was “Now it’s off to work,” potential thieves knew he would not be at home.
Security experts and privacy advocates have recently begun warning about the potential dangers of geotags, which are embedded in photos and videos taken with GPS-equipped smartphones and digital cameras. Because the location data is not visible to the casual viewer, the concern is that many people may not realize it is there; and they could be compromising their privacy, if not their safety, when they post geotagged media online.
Mr. Savage said he knew about geotags. (He should, as host of a show popular with technology followers.) But he said he had neglected to disable the function on his iPhone before taking the picture and uploading it to Twitter.
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Indeed, disabling the geotag function generally involves going through several layers of menus until you find the “location” setting, then selecting “off” or “don’t allow.” But doing this can sometimes turn off all GPS capabilities, including mapping, so it can get complicated.
The Web site ICanStalkU.com provides step-by-step instructions for disabling the photo geotagging function on iPhone, BlackBerry, Android and Palm devices.
A person’s location is also revealed while using services like Foursquare and Gowalla as well as when posting to Twitter from a GPS-enabled mobile device, but the geographical data is not hidden as it is when posting photos.
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By downloading free browser plug-ins like the Exif Viewer for Firefox (addons.mozilla.org/en-US/firefox/addon/3905/) or Opanda IExif for Internet Explorer (opanda.com/en/iexif/), anyone can pinpoint the location where the photo was taken and create a Google map.
Moreover, since multimedia sites like Twitter and YouTube have user-friendly application programming interfaces, or A.P.I.’s, someone with a little knowledge about writing computer code can create a program to search for geotagged photos in a systematic way. For example, they can search for those accompanied with text like “on vacation” or those taken in a specified neighborhood.
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“There are so many places where people upload photos, like personal blogs and bulletin boards,” said Johannes B. Ullrich, chief technology officer of the SANS Technology Institute, which provides network security training and monitors the Internet for emerging security threats.
Protecting your privacy is not just a matter of being aware and personally responsible, said Mr. Sommer, the researcher. A friend may take a geotagged photo at your house and post it.
“You need to educate yourself and your friends but in the end, you really have no control,” he said, adding that he was considering writing a program to troll the Internet for photos with geotags corresponding to users’ home addresses.
“I’m beginning to think there may be a market for it.”
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