tiff2rgba: 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/tiff2rgba - from package: libtiff

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

On Debian possible default full paths are:

/usr/bin/tiff2rgba - from package: libtiff-tools

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

Error in other languages:
tiff2rgba: bevel nie gevind nie
tiff2rgba: comandă negăsită
tiff2rgba: comando não encontrado
tiff2rgba: commande introuvable
tiff2rgba: command not found
tiff2rgba: käsku ei ole
tiff2rgba: không tìm thấy lệnh
tiff2rgba: komanda nerasta
tiff2rgba: Kommando nicht gefunden.
tiff2rgba: kommandot finns inte
tiff2rgba: komut yok
tiff2rgba: nie znaleziono polecenia
tiff2rgba: níor aimsíodh an t-ordú
tiff2rgba: no se encontró la orden
tiff2rgba: no s'ha trobat l'ordre
tiff2rgba: opdracht niet gevonden
tiff2rgba: parancs nem található
tiff2rgba: perintah tidak ditemukan
tiff2rgba: príkaz nenájdený
tiff2rgba: příkaz nenalezen
tiff2rgba: команда не найдена
tiff2rgba: командата не е открита
tiff2rgba: 命令找不到
tiff2rgba: コマンドが見つかりません