These textures are copied from Minetest Game and MineClone2 projects

# Minetest Game (CC BY-SA 3.0)
mtg_gui_formbg.png

# MineClone2 (CC BY-SA 3.0)
mcl_inventory_button9.png
mcl_inventory_button9_pressed.png
mcl_base_textures_background9.png