scanimage: 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 CentOS possible default full paths are:

/usr/bin/scanimage - from package: sane-backends

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/scanimage - from package: sane-utils

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

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