ppmtoyuvsplit: 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/ppmtoyuvsplit - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/ppmtoyuvsplit - from package: netpbm

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

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