Make the hieghtmap in GIMP or Photoshop, Make sure it is GREYSCALE. For GIMP, go to Image, Then mode, And hit Greyscale, then save it. The size must be 513x523.
For Photoshiop im not sure how to do this.
Also, Heres a mistake i made for my first map. The Hieghtmap must go into C:/FeralHeart/Media/Terrains NOT your maps folder inside terrains. NOT in pictures. also, it MUST be PNG.