metapixel-imagesize: 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/metapixel-imagesize - from package: metapixel

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

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