img2png: 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/img2png - from package: wxPython

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

On Debian possible default full paths are:

/usr/bin/img2png - from package: python-wxtools

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

Error in other languages:
img2png: bevel nie gevind nie
img2png: comandă negăsită
img2png: comando não encontrado
img2png: commande introuvable
img2png: command not found
img2png: käsku ei ole
img2png: không tìm thấy lệnh
img2png: komanda nerasta
img2png: Kommando nicht gefunden.
img2png: kommandot finns inte
img2png: komut yok
img2png: nie znaleziono polecenia
img2png: níor aimsíodh an t-ordú
img2png: no se encontró la orden
img2png: no s'ha trobat l'ordre
img2png: opdracht niet gevonden
img2png: parancs nem található
img2png: perintah tidak ditemukan
img2png: príkaz nenájdený
img2png: příkaz nenalezen
img2png: команда не найдена
img2png: командата не е открита
img2png: 命令找不到
img2png: コマンドが見つかりません