(defun renumber-files ()
  "This function works within Dired or Directory Editor in GNU
  Emacs. It will rename bunch of files and renumber them
  automatically by date and number of the file. It is useful when
  you are renaming less important images or bunch of files with
  irrelevant file names."
  (interactive)
  (let* ((files (dired-get-marked-files))
     (count 1))
    (dolist (file files)
      (let* ((extension (file-name-extension file))
         (filename (format "%s-%06.f.%s" (format-time-string "%F") count extension)))
    (rename-file file filename)
    (setq count (+ count 1))))))