Some excellent tips however if you or a client has many images, I would not recommend changing the default directories structure. First, the search isn’t impacted by the images being in different directories. It’s a database search and not a server search through WordPress and numbers does up database queries. Second, most server Is have restrictions as to how many files can go into a single directory. I’ve had clients have terrible trouble over loading a single directory with too many files. For the casual blogger this isn’t a big deal. For photobloggers or image intensive sites, it is.