fitstopnm: command not found

Have You tried accessing the binary with the full path?

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/fitstopnm - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/fitstopnm - from package: netpbm

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