pbmtoascii: 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/pbmtoascii - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pbmtoascii - from package: netpbm

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

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