.GMBCK File Extension

Graphic file used by games created with Game Maker, a game development IDE published by YoYo Games; contains a collection of images that can be tiled in the background of a game scene; also stores the background's name and target image size.

GMBCK files are used by Game Maker for auto-generating in-game textures; they may be created and saved using the Background Properties window in Game Maker.