gamma4scanimage: 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/gamma4scanimage - from package: sane-utils

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

Error in other languages:
gamma4scanimage: bevel nie gevind nie
gamma4scanimage: comandă negăsită
gamma4scanimage: comando não encontrado
gamma4scanimage: commande introuvable
gamma4scanimage: command not found
gamma4scanimage: käsku ei ole
gamma4scanimage: không tìm thấy lệnh
gamma4scanimage: komanda nerasta
gamma4scanimage: Kommando nicht gefunden.
gamma4scanimage: kommandot finns inte
gamma4scanimage: komut yok
gamma4scanimage: nie znaleziono polecenia
gamma4scanimage: níor aimsíodh an t-ordú
gamma4scanimage: no se encontró la orden
gamma4scanimage: no s'ha trobat l'ordre
gamma4scanimage: opdracht niet gevonden
gamma4scanimage: parancs nem található
gamma4scanimage: perintah tidak ditemukan
gamma4scanimage: príkaz nenájdený
gamma4scanimage: příkaz nenalezen
gamma4scanimage: команда не найдена
gamma4scanimage: командата не е открита
gamma4scanimage: 命令找不到
gamma4scanimage: コマンドが見つかりません