gif2png: 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/gif2png - from package: gif2png

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

Error in other languages:
gif2png: bevel nie gevind nie
gif2png: comandă negăsită
gif2png: comando não encontrado
gif2png: commande introuvable
gif2png: command not found
gif2png: käsku ei ole
gif2png: không tìm thấy lệnh
gif2png: komanda nerasta
gif2png: Kommando nicht gefunden.
gif2png: kommandot finns inte
gif2png: komut yok
gif2png: nie znaleziono polecenia
gif2png: níor aimsíodh an t-ordú
gif2png: no se encontró la orden
gif2png: no s'ha trobat l'ordre
gif2png: opdracht niet gevonden
gif2png: parancs nem található
gif2png: perintah tidak ditemukan
gif2png: príkaz nenájdený
gif2png: příkaz nenalezen
gif2png: команда не найдена
gif2png: командата не е открита
gif2png: 命令找不到
gif2png: コマンドが見つかりません