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 Madrid.JPG
Creation Date2011-07-16 14:47:16
File Size198,884 bytes (194.2 KB)
Dimensions1024 x 765 pixels
GPS Coordinates 40.42017, -3.68817