create floppy disk images on MacOS

I want to archive old floppy disks for archive.org. the easiest way is to create a floppy image, which also includes the boot records on bootable floppies.
the image then can be opened in DOS box or on MacOS (just rename to .dmg an open in Finder).

diskutil list
(find device of the floppy, ie /dev/disk2)
diskutil unmountDisk /dev/disk2
sudo dd if=/dev/disk2 bs=512 conv=noerror,sync of=myfloppy.img

and for CDs / DVDs

diskutil unmountDisk /dev/disk2
sudo dd if=/dev/disk2 bs=2048 conv=sync,notrunc of=myISO.iso