pnmstitch: 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/pnmstitch - from package: netpbm-progs

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

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