wordpress-avatar-custom-theme.php

<?php
/**-------------------------------------------
* @package WordPress Default Avatar
* @link http://rhythmshahriar.com
* @author Rhythm <rhy@rhythmshahriar.com>
* @copyright Copyright (c) 2013, Rhythm Shahriar
-------------------------------------------------*/
//**Custom Gravatar for Custom Themes**/
add_filter( 'avatar_defaults', 'rhythm_custom_gravatar' );
function rhythm_custom_gravatar ($avatar_defaults) {
$myavatar = get_bloginfo('template_directory') . '/images/custom-avatar.png'; // Image location, It's in your stylesheet image directory
$avatar_defaults[$myavatar] = "Rhythm"; // Name of your Avatar
return $avatar_defaults;
}