When you are using Shortcodes where you can insert images like the Picture Frames or Galleries you must use images that have been uploaded to your Media Library inside WordPress.
This is because we use a PHP Image Resizer called TimThumb. It is a simple, flexible, PHP script that resizes images. The version of TimThumb that we are using doesn’t allow you to use external images.
However we expect to include this feature in the next upgrade.