gthumb-importer: 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/gthumb-importer - from package: gthumb

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

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