It should possible in principle to create a "printer" in Life that constructs a rectangular region filled with repeated stable objects (like blocks) or nothing,

It should possible in principle to create a "printer" in Life that constructs a rectangular region filled with repeated stable objects (like blocks) or nothing, or some dithered density. If you are ok that it could never reach better than 50% density, you could encode your arbitrary image into an incoming stream (say, of gliders) that program the printer to make an arbitrary image. Similar to the way Von Neumann's self-reproducing cellular automaton produces itself from a "tape" of cells.