kiiski

  ;; There probably are better solutions already 
  ;; available somewhere.
  (defun org-insert-screenshot (filename)
    (interactive "sFilename: ")
    (let ((filename (concat filename ".png")))
      ;; import is from ImageMagick, change to whatever you like to use
      (call-process "import" nil nil nil filename)
      (insert (format "[[file:%s]]" filename))
      (org-display-inline-images)))