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 Golden Gate.JPG
Creation Date2012-03-27 14:07:36
File Size184,640 bytes (180.3 KB)
Dimensions1024 x 768 pixels
GPS Coordinates 37.80817, -122.4765