dvdvideo-backup-image: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/dvdvideo-backup-image - from package: python3-dvdvideo

You may install the required package with command apt-get install {package}

Error in other languages:
dvdvideo-backup-image: bevel nie gevind nie
dvdvideo-backup-image: comandă negăsită
dvdvideo-backup-image: comando não encontrado
dvdvideo-backup-image: commande introuvable
dvdvideo-backup-image: command not found
dvdvideo-backup-image: käsku ei ole
dvdvideo-backup-image: không tìm thấy lệnh
dvdvideo-backup-image: komanda nerasta
dvdvideo-backup-image: Kommando nicht gefunden.
dvdvideo-backup-image: kommandot finns inte
dvdvideo-backup-image: komut yok
dvdvideo-backup-image: nie znaleziono polecenia
dvdvideo-backup-image: níor aimsíodh an t-ordú
dvdvideo-backup-image: no se encontró la orden
dvdvideo-backup-image: no s'ha trobat l'ordre
dvdvideo-backup-image: opdracht niet gevonden
dvdvideo-backup-image: parancs nem található
dvdvideo-backup-image: perintah tidak ditemukan
dvdvideo-backup-image: príkaz nenájdený
dvdvideo-backup-image: příkaz nenalezen
dvdvideo-backup-image: команда не найдена
dvdvideo-backup-image: командата не е открита
dvdvideo-backup-image: 命令找不到
dvdvideo-backup-image: コマンドが見つかりません