pnmcrop: 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/pnmcrop - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pnmcrop - from package: netpbm

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

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