There's a few things I see here which might be worth checking. First, scale. The single-sided square at 100% scale is, give or take a bit, about ten inches square. The scale figures have nothing to do with the number of pixels, but the proportions of the square should match those of the image you want to put on it. Second, if you don't want shadows on the background, use Ambient Color rather than Diffuse Color. Third, remember to rotate the square to face the camera.