Big Brother has arrived, in case you missed it. In fact, you probably did miss it.

Those images you’ve been uploading to the web — your amusing YouTube video, the car-for-sale pictures on Craigslist, the TwitPic updates — may be embedded with coding that can reveal where the picture was taken, according to a report from the International Computer Science Institute, an independent, non-profit research institute in the United States.

GPS-equipped smart phones, iPhones and digital cameras embed location information in photos as a service to users to help them locate, sort and identify pictures. But most people either don’t know about the embedding or don’t understand how it can be abused, according to report co-author Robin Sommer.

Even tech-savvy users find it difficult to accurately assess the risk they face. As an example, the authors point to Apple’s iPhone 3G, which embeds high-precision geo-coordinates with all photos and videos taken with the internal camera unless explicitly switched off.

In fact, it is mostly devices at the higher end of the price scale that are geo-tagging, according to the report.

Some sites, including Facebook, strip the information from the photos in the process of uploading them onto the site. Others, like TwitPic and Craigslist, do not.

YouTube uses the geographic information by default. Flickr requires users to opt in if they want to share their location with others.

According to Flickr, there are currently 130-million geo-tagged photos and videos on the site.

Cracking the coded information is as simple as downloading free software. When used in conjunction with publicly available information like Google Street View, the information can be used to pinpoint home addresses or track a person’s movements over a period of weeks or months. It can be done in minutes.

It offers predators the ability to track potential victims and provides police and other public and private agencies with powerful investigative tools.

Sommer and his colleague Gerald Friedland were able to find the private addresses of celebrities, as well as the origins of Craigslist postings in which the poster wished to remain anonymous.

“We just basically put ourselves into the position of somebody who might want to exploit that in some form,” says Friedland.

The industry is currently pushing people to include geo-tags wherever they can, says Friedland. The number of online services collecting, providing and analyzing geo-information is growing. Websites like Foursquare, for example, encourage users to constantly update their location status.

A young female blogger who now prefers to remain anonymous, blogged about how a stranger tracked her down by phone at a restaurant with friends by following her Foursquare posts. She has withdrawn from the public eye after receiving a detailed death threat, she told the Star.

“In reality people should be much more comfortable going through a body scanner at the airport than uploading a precisely geo-tagged home video to the Internet,” says Friedland. “The reverse seems to be true.”

Internet security expert Larry Pesce learned about geotags from personal experience, after posting a picture of his infant daughter to Flickr. It wasn’t until a few months later, while conducting research on a related topic, that he learned the picture contained coding giving away the location of the shot.

Fortunately, Pesce says, he was on vacation at the time, and the location information was inaccurate.

Pesce and his friend Ben Jackson (they met on Twitter), founded icanstalku.com in May to educate people.

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“It’s quite possible to build up a database on people that is quite Big Brotherish,” says Jackson, who cites the dystopian novel 1984 by George Orwell as required reading for internet security experts.

Pesce, Jackson and the researchers at ICSI independently arrived at many of the same conclusions. They estimate that about three per cent of photos they sampled on various sites had geotags attached to them.

“It doesn’t sound like a lot, but when you’re talking about the number of photos posted in a day to Twitter, it’s still a sizeable amount of imagery,” says Pesce.

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