pamditherbw: 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/pamditherbw - from package: netpbm-progs

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

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