ppmtoeyuv: 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/ppmtoeyuv - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/ppmtoeyuv - from package: netpbm

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

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