gifrsize: 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/gifrsize - from package: giflib-utils

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

On Debian possible default full paths are:

/usr/bin/gifrsize - from package: giflib-tools

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

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