pngphoon: 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/pngphoon - from package: pngphoon

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

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