Gzip is used for compressing your text files including text, html, php, js and css. There is no need to gzip images for they are already compressed and gzipping them will cause extra server work.
Speed up site with Gzip & PHP
Use the following code at the top of your php files to gzip your page.
Place this at the top of your htaccess file. BE SURE TO REPLACE EXAMPLE.COM WITH YOUR DOMAIN ON LINE 2 & 3:
Speed up site with Gzip & Htaccess
Use the following code in your Htaccess file: (linux and unix servers ONLY)