Allow people to upload a few images at a time, and also give a url where a url can be downloaded (auto comment saying where the url was downloaded from?)
Allowing images to be grabbed directly from a website could see legal trouble with Copyright infringement. The idea currently is that people need to ensure the images aren't copywritten, or they own the Copyright on the image. The uploader agrees to indemnify the hosts and webpage against any such issues.
Grabbing a picture from another website bypasses these requirements.