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 New York.JPG
Creation Date2012-05-24 14:41:24
File Size309,350 bytes (302.1 KB)
Dimensions1024 x 768 pixels
GPS Coordinates 40.705, -74.013