Could you outline the image of the person and maybe do some sort of fill in the background? I would definitely use a very find thread like invisifil or silk for this so as not to detract. Additionally you may get away without quilting at all if it is just a wall hanging and will not be washed. Washing is what breaks down the integrity of batting. Or use a batting you can leave up to 10" unquilted like W&N, quilters Dream Poly, or dream green.