ppmtotga: 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 Debian possible default full paths are:

/usr/bin/ppmtotga - from package: netpbm

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

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