Stitched terrain.png

 stitched_terrain.png  was a texture atlas generated by the game in .minecraft, comprised of the game's block textures.

Whether it was actually used for block textures is unknown, as it can be removed from .minecraft at runtime seemingly without affecting the game. In addition, a sister atlas, stitched_items.png, has several invisible pixels shown at full intensity. As such, this atlas may just be a debugging byproduct - more information is needed on this matter. Its renaming to debug.stitched_terrain.png in 13w09a further supports this theory.