compatible.im(A, B, tol=1e-6)"im").TRUE if the images are compatible, and FALSE
  if they are not.A and B
  have compatible pixel dimensions. They are compatible if they have
  the same number of rows and columns, the same physical pixel
  dimensions, and occupy the same rectangle in the plane.  The argument tol specifies the maximum tolerated error
  in the pixel coordinates, expressed as a
  fraction of the dimensions of a single pixel.