The web has opened up new opportunities for stalkers: celebrities' home addresses are becoming easy to figure out because the stars aren't taking care when they upload pictures online. And tech-savvy thieves could even find out when they – or you – are away from home.
So say a group of US computer scientists, who have shown that address information can be gleaned from photo and video sharing sites. That's because many images and videos now contain geo-tags – latitude and longitude data. Often these are added automatically to material captured by devices such as smartphones.
To illustrate how easy it is to get this information, Gerald Friedland and Robin Sommer at the International Computer Science Institute in Berkeley, California, have created software that identifies YouTube videos shot close to their institute and tagged with words like "home". In some cases the location data embedded in the videos was precise enough to identify the house where it was shot.
The software then looked to see whether the same users had recently uploaded videos made more than 1500 kilometres away. Twelve people who were then away from their homes were identified, says Friedland, including one video title that made it clear it was the first day of the poster's vacation.
Still images also pose a risk. ICanStalkU.com, which went live in May, is designed to raise awareness of the privacy risks of geo-tagged images. The software behind the site looks for location data in images shared on Twitter. It then runs that data through Geonames, an online service that finds place names associated with latitude and longitude coordinates. The result is a stream of messages that identify the current location of Twitter users.
By tracking images posted on Twitter by a single user it is also possible to plot that user's movements on a map, say Ben Jackson and Larry Pesce, security consultants based in Boston and Providence, Rhode Island, respectively, and the creators of the site. Jackson says he will unveil this mapping tool next week at the Hackers on Planet Earth conference in New York.
Both teams of researchers said it was easy to find the home addresses of celebrities by looking at content they had shared online. Altogether the two groups claim to have located the homes of a famous sci-fi actor, a star musician and two television hosts.
The problem could be minimised if smartphones allowed users to vary the precision of location data, suggests Friedland. Images taken at home could be tagged with data that only identified the city, for example. Or users may simply prefer to turn the location data function off.