An attempt to help with some layer noise/artifacts that may be due to lithophanes flexing while printing vertically. Also, just support for same to help prevent failed prints.
Helpers are 100mm tall by default. Scale on the Z axis to match your lithophane (ie for a 130mm tall litho, scale Z by 130% or 1.30). Avoid scaling on X or Y as well unless you really want the tabs and legs thicker and longer.
Place two helpers on either end of the litho. just touching each edge litho. model. Tabs should just make contact with the edge of the model. Helpers can be cut away when print is completed.