Remote Images Grabber plugin fetches images from an URL or a piece of html-code, saves them directly into your blog media directory, and attaches to the appointed post.
Use this plugin instead of saving images from the internet and uploading them to your blog. You learn the value of this grabber e.g. when you need to move your old non-WordPress site with many pictures to the WordPress-based.
Download: http://wordpress.org/extend/plugins/remote-images-grabber/