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 Las Vegas.JPG
Creation Date2012-05-30 22:37:28
File Size211,570 bytes (206.6 KB)
Dimensions1024 x 768 pixels
GPS Coordinates 36.11033, -115.17317