A friend showed me a video from a Missouri news station (from a newscast almost 3 years ago, mind you). In the video, the reporters discuss a "new threat" with "new technology." While the video engages in the usual FUD (fear, uncertainty, and doubt) to oversell the risk, there is a nugget of truth that bears repeating.
Smartphones, tablets, and many standalone digital cameras have a GPS built-in, and can "geo-tag" photos with the location at which they were taken. This can make it easy to group photos by location (as in, group all my photos from the Grand Canyon, or from Disney World, or from Jamaica ... assuming I had vacationed at any of these places). But it makes it equally easy for someone else to do the same.