jhead: 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/jhead - from package: jhead

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

On Debian possible default full paths are:

/usr/bin/jhead - from package: jhead

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

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