The script works, and at the end, I have no .img file.
0+0 enregistrements lus
0+0 enregistrements écrits
0 octet (0 B) copié, 0,000541969 s, 0,0 kB/s
!!! The following error/warning messages can be ignored !!!
P: Mounting /dev/loop1 with offset 0
Warning: The resulting partition is not properly aligned for best performance.
dd: impossible d'ouvrir « chroot/usr/lib/syslinux/mbr.bin »: Aucun fichier ou dossier de ce type
P: Begin unmounting filesystems...
P: Saving caches...
Reading package lists... Done
Building dependency tree
Reading state information... Done
I am using Debian 8.4 and live-build 4.0.3-1.