vipsthumbnail: 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 Debian possible default full paths are:

/usr/bin/vipsthumbnail - from package: libvips-tools

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

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