ilbmtoppm: 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/ilbmtoppm - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/ilbmtoppm - from package: netpbm

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

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