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 Portimao.JPG
Creation Date2011-05-08 13:45:12
File Size152,280 bytes (148.7 KB)
Dimensions1024 x 765 pixels
GPS Coordinates 37.22983, -8.6295