Nowadays every photo taken with a mobile phone or digital camera contains metadata. This metadata, called Exif data, contains information about your camera, like brand and model name, the dimensions of the image and - when available - also GPS coordinates which reveal the location where the picture was taken.
File NameExample Niagara Falls.JPG
Creation Date2012-05-25 20:39:22
File Size386,200 bytes (377.1 KB)
Dimensions2014 x 1511 pixels
GPS Coordinates 43.08517, -79.07983