Sorting Photogravure stamp from litho is not to difficult as all photo stamps are printed by a series of tiny dots. Under magnification they are easily seen especially in and around the margins, the Queens portrait and the value tablet. The pattern of dots show up as uneven edges.
Litho stamps on the other hand have crisp clear lines to these features.
Recent gravure issues were originally chemically etched and the stamps showed a clearer image. These were then modified to the most recent method EME or computer etched these computer etched stamps show a clearer sharper picture. Similarly the process of photo restoration can be used to improve the quality of old photographs.
EME is short for Electro Mechanically Etched.
Four directions of print have been used, Sideways left or sideways right, upright and inverted. To determine the direction of print on photogravure stamps again a good lens is required, the tiny dots (or points) show up as pointing in the print direction. Check it out, something for the beginner to do on a cold winter night perhaps!