ppmtompeg: 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/ppmtompeg - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/ppmtompeg - from package: netpbm

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

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