idevicescreenshot: 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/idevicescreenshot - from package: libimobiledevice-utils

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

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