gmerlin_imgconvert: 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
/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/gmerlin_imgconvert - from package: gmerlin

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