simple-image-reducer: 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 Debian possible default full paths are:

/usr/bin/simple-image-reducer - from package: simple-image-reducer

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

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