tiffdiff: 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/tiffdiff - from package: lcms

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

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