Custom WordPress Default Avatar

avatar.php

<?php
function custom_gravatar ( $avatar_defaults ) {
  $mytavatar = get_theme_directory_uri . '/images/avatar.jpg'; // Make Sure you change this depending on your image name and location
  $avatar_defaults[ $mytavatar ] = 'My Custom Gravatar'; // This is what is displayed in the Admin settings when Picking your Default Avatar
  
  return $avatar_defaults;
}

add_filter( 'avatar_defaults', 'custom_gravatar' );