jpegtran: 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/jpegtran - from package: libjpeg-turbo

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

On Debian possible default full paths are:

/usr/bin/jpegtran - from package: libjpeg-turbo-progs

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

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