pnmtorle: 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/pnmtorle - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pnmtorle - from package: netpbm

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

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