"I like to take a lot of photos of my dog and post them on Twitter. I think she's really cute. Also my friends and family," said Parker.
But one day she got an ominous Tweet from the website Icanstalku.com telling her they know where she lives.
"I thought it was a little scary. They were accurate to my location from my house. So my immediate response was, 'What happened, how do you know where I am?'" said Parker.
Turns out Parker's photos contained GPS information called "geotags" embedded by her smart phone. Every time she posted a photo online that she took with her phone, she was inadvertently giving out her whereabouts.
"And the location can be as accurate as plus/minus one meter, depending on the reception of the GPS signal of the device you're using," said Gerald Friedland, International Computer Science Institute of Berkeley.
Friedland co-authored a study on the privacy implications of geotagging. The findings: Most people had no idea what they were posting online.
"There's enough information out there that you can actually track people and do potential harm to them," said Friedland.
That's exactly what Larry Pesce wants to warn people about. He co-founded Icanstalku.com to alert people after he discovered a photo of his child revealed her location. And it can happen to others.
"For example, let's take a picture of your nice brand-new 50-inch plasma TV at your house and you're now sharing the location of that TV and an hour later you're posting a photograph from the 7-Eleven and now we know that you're not home," said Pesce.
In addition to potential robberies, Pesce says geotagged photos open up the possibility of stalking and domestic violence. And you don't have to be some expert to get the information.
"Just about anybody that can operate a computer and do a couple of right-clicks could find out someone's location," said Pesce.
Both Pesce and Friedland hope to make more people aware of this potential privacy issue.
"Going forward we're going to start sharing more and more about our lives online and we really want folks to make sure that they know what they're sharing," said Pesce.
"I don't think many people know they're Tweeting their geographic information every time they post a photo," said Christina Parker.
So what can you do about it? You don't have to stop posting pictures. Just turn off the GPS feature for photos on your phone. It won't affect the other GPS capabilities.