HY2328 : Brough of Birsay
The cliffs in the far distance are called Veniba (not Loop of Crooie) and are indeed in grid square
HY2729. However the photograph was taken from grid
HY2328 giving rise to an interesting question - "is the grid reference meant to indicate the point from which the picture was taken (the point of view) or the most distant subject?"
The Loop of Kroo or Crooie (as marked on the OS map) is the curving indentation just west of the cliffs of Veniba.