GIF Signature

 The following GIF Signature identifies  the  data  following  as  a
 valid GIF image stream.  It consists of the following six characters:

   G I F 8 7 a

 The last three characters '87a' may be viewed as a  version  number for
 this  particular  GIF  definition  and will be used in general as a
 reference  in  documents  regarding  GIF  that   address   any   version
 dependencies.