Add Your Own Default Avatar to WordPress

functions.php

<?php
function new_avatar( $avatar_defaults ) {
    $new_avatar = content_url() . '/uploads/[your image]';
    $avatar_defaults[ $new_avatar ] = 'No Avatar';
    return $avatar_defaults;
}
add_filter( 'avatar_defaults', 'new_avatar' );
?>

Is there a fun image you'd like to use as the default user image if they don't have a Gravatar? This is what you need - just add the code to your theme's functions.php, replace [your image] with the name of the image in your uploads folder.