//get domain from url
function get_domain($url) { 
/*
Author : Ayush
URL : http://Webgarb.com
*/
    $url = explode('/', str_replace('www.', '', str_replace('http://', '', $url)));
    return $url[0];
}
 
//get favicon from google and cache it
function getFavicon($var){
    $cache_days = 30; 
    $linkdomain = get_domain($var);
    $favicon_cache_dir = ABSPATH.'wp-content'.DIRECTORY_SEPARATOR.'plugins'.DIRECTORY_SEPARATOR.'favicon_cache';
    $favicon_url = 'http://www.quakemachinex.com/blog/wp-content/plugins/favicon_cache/'.$linkdomain.'.png';
    $fp = fopen ($favicon_cache_dir.'/'.$linkdomain.'.png', 'r');
    $favicon_create_time = filectime($favicon_cache_dir.'/'.$linkdomain.'.png');
    $time_now = date("Y-m-d H:i:s");
    $favicon_stay_days = (strtotime($time_now)-strtotime(date("Y-m-d H:i:s",$favicon_create_time)))/86400;
    $favicon_stay_days = floor($favicon_stay_days);
   
    if ($fp && $favicon_stay_days < $cache_days) {
        return $favicon_url;
     } else {
        $remote_favicon = file_get_contents('http://www.google.com/s2/favicons?domain='.$linkdomain);
        $local_favicon = $favicon_cache_dir.'/'.$linkdomain.'.png';
        $local_favicon_actual = fopen($local_favicon, 'w+');
        fwrite($local_favicon_actual, $remote_favicon);
        fclose($local_favicon_actual);       
        return $favicon_url;
     }
      
}

http://www.quakemachinex.com/blog/

Cache favicon from google service

php, google, cache

PHP