You can create a blank floppy image with the command:

mkfs.msdos -C /path/imagefile.img 1440

On some systems /mkfs.msdos is under /sbin directory. Afterwards you can mount it as loopback device with command:

sudo mkdir /media/floppy1/

sudo mount -o loop /path/imagefile.img /media/floppy1/

To unmount, use the command

sudo umount /media/floppy1/

If you want to create an image from the physical floppy disk, use dd command (disclaimer - I didn't try the below as my floppy is gone! but should work) (and assume that's 1.44MB type floppy disk... 1.2MB ones should have gone at the time of DOS 6.22 )

dd bs=512 count=2880 if=/dev/fda of=/path/imagefile.img

Reference: man page of mkfs.msdos; Create mount and copy floppy disks images under linux