The file format known as JPEG Interchange Format (JIF) is specified in Annex B of the standard. However, this “pure” file format is rarely used, primarily because of the difficulty of programming encoders and decoders that fully implement all aspects of the standard and because of certain shortcomings of the standard:
Color space definition
Component sub-sampling registration
Pixel aspect ratio definition
Image files that employ JPEG compression are commonly called JPEG files. Most image capture devices (such as digital cameras) and most image editing software programs that output JPEG files are actually creating a file in the JFIF and/or Exif format．
The most common filename extensions for files employing JPEG compression are .jpg and .jpeg, though .jpe, .jfif and .jif are also used. It is also possible for JPEG data to be embedded in other file types - TIFF encoded files often embed a JPEG image as a thumbnail of the main image.