The .OBJ files are sprites that represent the object visible in the game. The frames in the sprite are the faces of the object that are visible from different directions. An OBJ can has as few as one sprite frame (barrels, pedestals, trees) or as many as 24 for objects that are animated (mirror, tent) or have different states (chests). Some OBJ files will contain two separate objects that have a slight variation (pedestals). Information on which sprite frame corresponds to which cardinal direction and what frames are used to animate the object are stored in DARK.DAT File or CLOUDS.DAT File.
These images have been cropped in order to fit them on the screen. Images in gray scale are extrapolated from the animation information and are not actually stored in the OBJ file.