First, watch this. Very informative and at the same time alarming.
For tech geeks, this information is basic. But I'm thinking about just anybody else who has a smartphone and posting their pictures online. You should know that your phone is producing geographical locations embedded on your pictures' metadata. This enables practically anyone who knows about this to track you down through the picture you posted.
Here's a guide on how to turn off your phone's location settings from ICanStalkU.com.