cthumb: 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/cthumb - from package: cthumb

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

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