NAME: ImageSize

     USE: Function to return the size in bytes necessary to store the
          specified image.  This function is used primarily with the
          GetImage procedure to determine the exact size needed to hold
          a selected area.

     DEPENDENCY:  Must first be in graphics mode.  The unit Graph
                  must also be placed in the uses section.

     SYNTAX: ImageSize(X1, Y1, X2, Y2 : Word);