convert_image: 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/convert_image - from package: CBFlib

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

On Debian possible default full paths are:

/usr/bin/convert_image - from package: cbflib-bin

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

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