gifcomb: 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/gifcomb - from package: giflib-utils

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

On Debian possible default full paths are:

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

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

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