gnome-screenshot: 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/gnome-screenshot - from package: gnome-utils

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

On Debian possible default full paths are:

/usr/bin/gnome-screenshot - from package: gnome-screenshot

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

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