(defun my/generate-qr (text &optional img)
  "Generate a QR code from the region or given TEXT.

If no region is active, the TEXT defaults to the clipboard content.

When IMG is non-nil, generate an image instead of the default
UTF-8 representation.

This function relies on qrencode(1) being present in your $PATH."
  (interactive
   (let ((default-text (if (use-region-p)
                           (buffer-substring-no-properties (region-beginning) (region-end))
                         (my/clipboard-get))))
     (list
      (read-string (format-prompt "Text" default-text) nil nil default-text)
      current-prefix-arg)))
  (with-current-buffer (get-buffer-create "*qr*")
    ;; in case the buffer still exists and image-mode is active
    (fundamental-mode)
    (read-only-mode -1)
    (erase-buffer)
    (insert text)
    (let ((file-format
           (if (equal current-prefix-arg '(4)) "PNG" "UTF8")))
      (call-process-region nil nil "qrencode" t t nil "-o" "-" "-t" file-format)
      (when (and (display-graphic-p) (string= file-format "PNG"))
        (image-mode)))
    (read-only-mode)
    (display-buffer (current-buffer))))