convert4chan: 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/convert4chan - from package: ir.lv2

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

Error in other languages:
convert4chan: bevel nie gevind nie
convert4chan: comandă negăsită
convert4chan: comando não encontrado
convert4chan: commande introuvable
convert4chan: command not found
convert4chan: käsku ei ole
convert4chan: không tìm thấy lệnh
convert4chan: komanda nerasta
convert4chan: Kommando nicht gefunden.
convert4chan: kommandot finns inte
convert4chan: komut yok
convert4chan: nie znaleziono polecenia
convert4chan: níor aimsíodh an t-ordú
convert4chan: no se encontró la orden
convert4chan: no s'ha trobat l'ordre
convert4chan: opdracht niet gevonden
convert4chan: parancs nem található
convert4chan: perintah tidak ditemukan
convert4chan: príkaz nenájdený
convert4chan: příkaz nenalezen
convert4chan: команда не найдена
convert4chan: командата не е открита
convert4chan: 命令找不到
convert4chan: コマンドが見つかりません