Function ImageSize(X1,Y1,X2,Y2:LongInt):LongInt;

    Returns the  memory  requirements  for  a  sprite  (PutImage).   Note
    that if you are not using  one  of  the  16, 256, 32 k or 64 k colour
    modes  (like  say  a  2   colour    mode),   you  will  have  to  use
    Graph.GetImage or add some code to the unit.

    If you would like to use this procedure, make sure that

    {$DEFINE UsingGraph}

    is placed at the  top  of  the  file.   If  you  are  not  using this
    procedure, you can save some code space by placing

    {$DEFINE NotUsingGraph}

    at the top of the file.