pamaddnoise: 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/pamaddnoise - from package: netpbm-progs

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

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