pbmtpg: 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/pbmtpg - from package: pnm2ppa

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

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