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 Denver.JPG
Creation Date2012-01-08 12:58:45
File Size303,412 bytes (296.3 KB)
Dimensions1024 x 768 pixels
GPS Coordinates 39.74633, -105.02483