title: Form File-Upload from URL or Data-URL?
body: <p>Can I use an <code>&lt;input type="file"&gt;</code> field with an (data)URL?</p>
  
  <p>I would need something like this in an Greasemonkey-script, but it seems impossible.
  Or is there some way?</p>
  
  <p>The only working alternative seems at the moment trying to write a proxy, which replaces the file-field with an text-field for an URL, so the proxy can download the file, and submit the form. But this is too complicated in contrast to a Greasemonkey-script.</p>
  
  <p>I want to add to some sites a "select a preset image" at the position of the filechooser.</p>
  
  <p>As JavaScript cannot access the disk to save an image and then select it for uploading again, it would need to be done by data-URL's or something like this.</p>