findimagedupes: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/findimagedupes - from package: findimagedupes

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