ppmtomap: 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/ppmtomap - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/ppmtomap - from package: netpbm

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

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