tiffdither: 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/tiffdither - from package: libtiff

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

On Debian possible default full paths are:

/usr/bin/tiffdither - from package: libtiff-tools

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

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