showimage: 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/showimage - from package: SDL_image

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

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