I think they might not have been 513 by 513, as I was making a template for a different website. They were all .png files, and were saved in Feralheart > Media > Terrains. I'd also used GIMP- however, since I turned my comp off for night/school, it may work now that it has restarted. <3 I hope it does, as one of the height maps I love.
EDIT: I looked in my Terrains folder, the pictures went poofie o3o but the game's working now, at least. Thanks for trying to help! ;3