imgvview: 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/imgvview - from package: imgvtopgm

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

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