pnmtile: 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/pnmtile - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pnmtile - from package: netpbm

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

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