function dm_get_avatar( $avatar, $id_or_email, $size ) {

 $sayi=rand(1,35);
$avatar='<img src="'.bloginfo("template_url").'/klasorler/isim-'.$sayi.'.jpg" alt="Rastgele Avatar" rel="noindex nofollow" class="avatar avatar-60 photo" width="'.$size.'" height="'. $size.'"/>';
 return $avatar;
}
add_filter( 'get_avatar', 'dm_get_avatar', 10, 32 );