Make a 3 Gb image:

dd if=/dev/zero of=debian.img bs=1M count=3072

Format the image to ext3

mkfs.ext3 -F debian.img

Make two directorys to mount the images in

mkdir rootfs
mkdir debian

sudo mount -o loop rootfs.img ./rootfs

sudo mount -o loop debian.img ./debian

Copy all the contents from one image to another and preserve owners and rights

sudo cp -pr ./debian/* ./rootfs