pnmscalefixed: 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/pnmscalefixed - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pnmscalefixed - from package: netpbm

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

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