NSImageTest: 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/NSImageTest - from package: gnustep-examples

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

On Debian possible default full paths are:

/usr/bin/NSImageTest - from package: gnustep-examples

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

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