In a previous article I touched on the oEmbed standard and a little about the use of remote media including remote images.
Of course embedding images into to page whether hosted remotely or locally is not a new thing. Embedding remote images from the Drupal UI is not supported out of the box. Of course you can manually edit the html using your wysiwyg editor, but that is not very user friendly and is not a great user experience. Furthermore doing so increases that the risk your markup may be malformed etc