ilcontrast: command not found

Have You tried accessing the binary with the full path?

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/ilcontrast - from package: mono-tools-gui

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