It stands/prints quite happily on its edge.
The Lithophane has a border around the edge "Border (MM): 1.6" and is 10 mm thick and 199 mm long so it stood on a base 10 x 199 mm.
If you don't want a border, use the tool, specify a base and it will attach a base to the lithophane so that it will print on edge without a border.
If you want the base going out the back specify a negative number. http://3dp.rocks/lithophane