Ok!
I have clear now tath I want to goereference instead of orthorectiy. Anyway, software as ILWIS let you having into account a Terrain model in order to georeference image. Having x,y and z instead of x and y coordinates, helps IlWIS to correct distorsion derived from terrain. I know tath Erdas do this too. It's any way to include a DTM in arcgis to making georeferencing more accurate?
Thanks!