ppmtoleaf: 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/ppmtoleaf - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/ppmtoleaf - from package: netpbm

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

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