web2png: 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/web2png - from package: gif2png

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

Error in other languages:
web2png: bevel nie gevind nie
web2png: comandă negăsită
web2png: comando não encontrado
web2png: commande introuvable
web2png: command not found
web2png: käsku ei ole
web2png: không tìm thấy lệnh
web2png: komanda nerasta
web2png: Kommando nicht gefunden.
web2png: kommandot finns inte
web2png: komut yok
web2png: nie znaleziono polecenia
web2png: níor aimsíodh an t-ordú
web2png: no se encontró la orden
web2png: no s'ha trobat l'ordre
web2png: opdracht niet gevonden
web2png: parancs nem található
web2png: perintah tidak ditemukan
web2png: príkaz nenájdený
web2png: příkaz nenalezen
web2png: команда не найдена
web2png: командата не е открита
web2png: 命令找不到
web2png: コマンドが見つかりません