Recently, my mother sent me one of those news clips about how easy it was to find (read stalk) kids, just from a photo a parent took a smartphone and then posted it on some photo-sharing site. Like all of those news shorts, there was truth and hyperbole wrapped up in this piece she sent.
Smartphone cameras are amazing things; they can store all sorts of information with the pictures you take. Some of that information includes the date and time of the photo, camera settings used when taking the photo, and GPS coordinates (geotagging) of where that picture was taken. When you share that photo, as in emailing it to your friends, or posting it via some of the photo sharing sites, you might also be sharing some of that information. And, then someone can extract that information, specifically the GPS coordinates stored when that picture was taken, and map it. Do that with enough photos and someone with evil intentions could create a map of common daily actions for that child so they could pick up that child. But, plain old street work can easily accomplish the same with much less effort.
And, here is where my favorite to bash for privacy invasion, Facebook, actually does a good job. When you post a photo with Facebook, their posting process actually strips out most of this hidden information (called Exif if you want to look up more about it). Flickr seems to do a similar thing, also.
How do you find out if your photos on the web contain this information? Find the photo, save a copy to your computer and open it with your favorite image editor. Most will have some way to see this stored information. Or, you can right-click on an image and look at properties (in Windows) or use get info (in OSX) to see this Exif data. There are programs to erase or modify this data and then you would repost your photo(s). And, then you will have data about your whereabouts floating around on the Web.