When you shoot with your digital camera (any type for that matter) captures an image and stores the data on the memory card in digital format. Along with that photograph is also recorded some information regarding the image which can later be viewed using a computer or camera. This information is called EXIF. A long list of properties of the shot image is stored in the EXIF info few of which are: Camera make & model, Date, Time, Image size in megabytes, Image dimensions (height/width), Exposure time, F number, Exposure Program, ISO Speed, Exif Version, Shutter Speed Value, Aperture Value, Exposure Bias Value, Metering Mode, Flash (fired or not), Macro Mode, Self timer (on/off), Quality (setting in which photo was recorded) etc.

This additional information stored in the image file itself which can be recollected using EXIF reader softwares most of which are free to use and widely available online. Modern PC operating systems, image galleries (online/desktop) and image viewers are all equipped with EXIF readers. For details please see image below: