Skim through the photos on Flickr or Photobucket, and you'll find pictures of cats pawing at living-room sofas, children playing in backyards and mothers gardening at home.



Dig a little deeper, and you can unearth the exact locations of many of those homes, embedded in data within the pictures.

Images often contain a bundle of information and various traces left by digital cameras or photo manipulation software.

This data, called Exchangeable Image File Format (EXIF), is a key tool for many professionals. It can detail whether the photographer used a flash, which digital effects were applied to a picture and when the photo was taken.

EXIF can also contain the precise GPS coordinates for where a photo was taken. This information is readily accessible and can be plugged into software such as Google Maps -- leading some security and photography experts to express concerns about amateurs unknowingly disclosing private information, such as the location of their home.

"What could go wrong with that?" Roger Thompson, the chief research officer for digital security firm AVG, said sarcastically.

Thomas Hawk, an active Flickr user and the former chief executive of competing photo site Zooomr, said EXIF is an important part of his archival process. But he has also used that data to track down someone who was harassing him online and managed to coerce an apology, he said.

"I don't geotag any pictures to my house," Hawk said on the phone last week. "I think it's a huge concern. I think a lot of people don't realize or recognize what's in all of the EXIF data that they're publishing."

Most gadgets ignore the geotagging component of EXIF because relatively few cameras contain the GPS chips needed to tag them. However, many smartphones, such as those from Apple and Google's Android system, let users employ this feature.

Apple's and Google's systems ask each user once or a few times for permission to access their location in order to provide additional services. If they click "OK" on that popup, every photo they take is tagged with GPS coordinates.

Smartphones are fast becoming the camera of choice for many people. Cameras on newer phones have come to rival dedicated point-and-shoots, and many smartphone owners carry them just about everywhere. Smartphone sales have increased 50 percent since last year, according to a report by research firm Gartner...
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