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 Barcelona.JPG
Creation Date2012-10-24 16:37:44
File Size175,720 bytes (171.6 KB)
Dimensions1024 x 768 pixels
GPS Coordinates 41.37317, 2.1895