simple_dcraw: 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/simple_dcraw - from package: LibRaw-samples

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

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