tiff2bw: 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/tiff2bw - from package: libtiff

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

On Debian possible default full paths are:

/usr/bin/tiff2bw - from package: libtiff-tools

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

Error in other languages:
tiff2bw: bevel nie gevind nie
tiff2bw: comandă negăsită
tiff2bw: comando não encontrado
tiff2bw: commande introuvable
tiff2bw: command not found
tiff2bw: käsku ei ole
tiff2bw: không tìm thấy lệnh
tiff2bw: komanda nerasta
tiff2bw: Kommando nicht gefunden.
tiff2bw: kommandot finns inte
tiff2bw: komut yok
tiff2bw: nie znaleziono polecenia
tiff2bw: níor aimsíodh an t-ordú
tiff2bw: no se encontró la orden
tiff2bw: no s'ha trobat l'ordre
tiff2bw: opdracht niet gevonden
tiff2bw: parancs nem található
tiff2bw: perintah tidak ditemukan
tiff2bw: príkaz nenájdený
tiff2bw: příkaz nenalezen
tiff2bw: команда не найдена
tiff2bw: командата не е открита
tiff2bw: 命令找不到
tiff2bw: コマンドが見つかりません